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Safety at Rural Non-Signalized
Intersections in Delaware
By
REBECCA FREY
ARDESHIR FAGHRI
Civil and Environmental Engineering
University of Delaware
September 2012
Delaware Center for Transportation University of Delaware
355 DuPont Hall
Newark, Delaware 19716
(302) 831-1446
DCT 226
The Delaware Center for Transportation is a university-wide multi-disciplinary research unit reporting to the Chair of the Department of Civil and Environmental Engineering, and is co-sponsored by the University of Delaware and the Delaware Department of Transportation.
DCT Staff
Ardeshir Faghri Jerome Lewis Director Associate Director
Ellen Pletz Earl “Rusty” Lee Matheu Carter Sandra Wolfe Assistant to the Director T2 Program Coordinator T² Engineer Event Coordinator
DCT Policy Council
Natalie Barnhart, Co-Chair Chief Engineer, Delaware Department of Transportation
Babatunde Ogunnaike, Co-Chair Dean, College of Engineering
Delaware General Assembly Member
Chair, Senate Highways & Transportation Committee
Delaware General Assembly Member Chair, House of Representatives Transportation/Land Use & Infrastructure Committee
Ajay Prasad
Professor, Department of Mechanical Engineering
Harry Shenton Chair, Civil and Environmental Engineering
Michael Strange
Director of Planning, Delaware Department of Transportation
Ralph Reeb Planning Division, Delaware Department of Transportation
Stephen Kingsberry
Executive Director, Delaware Transit Corporation
Shannon Marchman Representative of the Director of the Delaware Development Office
James Johnson
Executive Director, Delaware River & Bay Authority
Holly Rybinski Project Manager-Transportation, AECOM
Delaware Center for Transportation University of Delaware
Newark, DE 19716 (302) 831-1446
Safety at Rural Non-Signalized
Intersections in Delaware
SEPTEMBER 15, 2012
By: Rebecca Frey
Table of Contents
1. Abstract…………………………………………………………………………………………1
2. Introduction……………………………………………………………………………………..3
3. Project Overview and Methodology…….……………………………………………………...5
4. Delaware 15 & Delaware 10……..……………………………………………………………..8
4.1. Site Overview and Site Visit Observations…………………………………………...8
4.2. Intersection Trends and Reason for Crash Analysis……...…………………………..9
4.3. Suggested Countermeasures and Projected Effectiveness………………………..…16
4.4. Cost/ Benefit Analysis………………………..……………………………………..17
5. Delaware 15 & Barratts Chapel Road………...……………………………………………….19
5.1. Site Overview and Site Visit Observations………………………………………….19
5.2. Intersection Trends and Reason for Crash Analysis…….…………………………..20
5.3. Suggested Countermeasures and Projected Effectiveness…………………..………26
5.4. Cost/ Benefit Analysis……………………………………..………………………..33
6. Delaware 15 & Andrews Lake Road…………………………….……………………………36
6.1. Site Overview and Site Visit Observations………………………………………….36
6.2. Intersection Trends and Reason for Crash Analysis……….………………………..37
6.3. Suggested Countermeasures and Projected Effectiveness………………..………....44
6.4. Cost/ Benefit Analysis…………………..…………………………………………..46
7. Delaware 30 & Mount Joy Road…………………………..………………………………….50
7.1. Site Overview and Site Visit Observations………………………………………….50
7.2. Intersection Trends and Reason for Crash Analysis…………………….…………..51
7.3. Suggested Countermeasures and Projected Effectiveness………………..…………57
7.4. Cost/ Benefit Analysis…………………………………..…………………………..58
8. Delaware 30 & Zoar Road……………………………...……………………………………..59
8.1. Site Overview and Site Visit Observations………………………………………….59
8.2. Intersection Trends and Reason for Crash Analysis……………….………………..61
8.3. Suggested Countermeasures and Projected Effectiveness…………..………………67
8.4. Cost/ Benefit Analysis………………………………………..……………………..69
9. Overall Observations and Conclusions……………………………………….……………….71
References………………………………………………………………………………………..72
List of Figures
Figure 1. Intersection locations……………………………………………………………………3
Figure 2. Delaware 10 and Delaware 15 location map…………………………………………....8
Figure 3. Delaware 15 and Barratts Chapel Road location map…………………………………19
Figure 4. Lane narrowing concept one (Source: Federal Highway Administration)…………….29
Figure 5. Field view of lane narrowing concept one
(Source: Federal Highway Administration)……………………………………………………...29
Figure 6. Lane narrowing concept two
(Source: Federal Highway Administration)……………………………………………………...30
Figure 7. Field view of lane narrowing concept two
(Source: Federal Highway Administration)……………………………………………………...30
Figure 8. Combined lane narrowing concept
(Source: Federal Highway Administration)……………………………………………………...31
Figure 9. Delaware 15 and Andrews Lake Road location map………………………………….36
Figure 10. Delaware 30 and Mount Joy Road location map……………………………………..50
Figure 11. Delaware 30 and Zoar Road location map…………………………………………...60
List of Tables
Table 1. Types of crash at Delaware 10 & Delaware 15……………………………………...…10
Table 2. Reason for crash summary at Delaware 10 & Delaware 15……………………………10
Table 3. Approach of driver responsible for crash at Delaware 10 & Delaware 15……………..11
Table 4. Crash severity summary at Delaware 10 & Delaware 15………………………………11
Table 5. Time of day of crash summary at Delaware 10 & Delaware 15……………………..…12
Table 6. Period of day of crashes at Delaware 10 & Delaware 15……………………………....12
Table 7. Day of week of crashes at Delaware 10 & Delaware 15……………………………….13
Table 8. Month of crash summary at Delaware 10 & Delaware 15……………………………..13
Table 9. Age of drivers responsible for crash at Delaware 10 & Delaware 15………………….14
Table 10. Age of all drivers involved in crashes at Delaware 10 & Delaware 15…………….…14
Table 11. Weather conditions during crashes at Delaware 10 & Delaware 15………………….15
Table 12. Road conditions during crashes at Delaware 10 & Delaware 15…………………..…15
Table 13. Alcohol related crashes at Delaware 10 & Delaware 15……………………………...15
Table 14. Crash reduction due to roundabout conversion at Delaware 10 & Delaware 15……...16
Table 15. Monetary value of crash reduction for roundabout conversion at
Delaware 15 & Delaware 10……………………………………………………………………..17
Table 16. Cost benefit analysis for roundabout at Delaware 10 & Delaware 15………………...18
Table 17. Type of crash summary for Delaware 15 & Barratts Chapel Road…………………...20
Table 18. Reason for crash summary at Delaware 15 & Barratts Chapel Road…………………21
Table 19. Approach of driver responsible for crash at Delaware 15 & Barratts Chapel Road…..21
Table 20. Crash severity summary at Delaware 15 & Barratts Chapel Road…………………....22
Table 21. Time of day of crashes at Delaware 15 & Barratts Chapel Road…………………..…22
Table 22. Period of day of crashes at Delaware 15 & Barratts Chapel Road……………………23
Table 23. Day of the week of crashes at Delaware 15 & Barratts Chapel Road………………...23
Table 24. Month of year of crashes at Delaware 15 & Barratts Chapel Road…………………...24
Table 25. Age of drivers responsible for crash at Delaware 15 & Barratts Chapel Road……….24
Table 26. Ages of all drivers involved in crashes at Delaware 15 & Barratts Chapel Road…….25
Table 27. Weather conditions during crashes at Delaware 15 & Barratts Chapel Road……...…25
Table 28. Road conditions during crashes at Delaware 15 & Barratts Chapel Road…………....25
Table 29. Alcohol related crashes at Delaware 15 & Barratts Chapel Road……………….……26
Table 30. Expected crash reduction for conversion to all way stop control at
Delaware 15 & Barratts Chapel Road…………………………………………………………....27
Table 31. Expected crash reduction for conversion to roundabout at
Delaware 15 & Barratts Chapel Road……………………………………………………………28
Table 32. Expected crash reduction for lane narrowing concept at
Delaware 15 & Barratts Chapel Road……………………………………………………………32
Table 33. Monetary value of crash reduction for all way stop conversion at
Delaware 15 & Barratts Chapel Road…………………………………………………………....33
Table 34. Monetary value of crash reduction for conversion to a roundabout at
Delaware 15 & Barratts Chapel Road…………………………………………………………....34
Table 35. Expected monetary value of crash reduction for lane narrowing concept at
Delaware 15 & Barratts Chapel Road……………………………………………………………34
Table 36. Cost to benefit ratio for proposed
Delaware 15 & Barratts Chapel countermeasures……………………………………………….35
Table 37. Type of crash at Delaware 15 & Andrews Lake Road………………………………..38
Table 38. Reason for crashes at Delaware 15 & Andrews Lake Road…………………………..38
Table 39. Approach direction of vehicle responsible for crash at
Delaware 15 & Andrews Lake Road…………………………………………………………….38
Table 40. Crash severity at Delaware 15 & Andrews Lake Road…………………………….…39
Table 41. Time of day of crashes at Delaware 15 & Andrews Lake Road………………………40
Table 42. Day and night crash summary for Delaware 15 & Andrews Lake Road……………..40
Table 43. Day of week of crashes at Delaware 15 & Andrews Lake Road…………………...…41
Table 44. Month of year of crashes at Delaware 15 & Andrews Lake Road……………………42
Table 45. Age of drivers responsible for crash at Delaware 15 & Andrews Lake Road………...42
Table 46. Age of all drivers involved in crashes at Delaware 15 & Andrews Lake Road……....43
Table 47. Weather during crashes at Delaware 15 & Andrews Lake Road……………………..43
Table 48. Road conditions during crashes at Delaware 15 & Andrews Lake Road……………..43
Table 49. Alcohol related crashes at Delaware 15 & Andrews Lake Road……………………...44
Table 50. Expected crashes with reduction of skew angle………………………………………45
Table 51. Expected crash reduction for addition of intersection lighting………………………..45
Table 52. Monetary value of crash reduction for removal of skew angle at
Delaware 15 & Andrews Lake Road…………………………………………………………….47
Table 53. Monetary value of crash reduction for installation of intersection lighting at
Delaware 15 & Andrews Lake Road………………………………………..…………………..47
Table 54. Cost estimate for intersection realignment at Delaware 15 & Andrews Lake Road….48
Table 55. Cost to benefit ratio for proposed Delaware 15 & Andrews Lake Road
countermeasures………………………………………………………………………………….49
Table 56. Type of crash summary at Delaware 30 & Mount Joy Road………………………….51
Table 57. Reason for crash summary at Delaware 30 & Mount Joy Road………………………52
Table 58. Approach of driver responsible for crashes at Delaware 30 & Mount Joy Road……..52
Table 59. Crash severity at Delaware 30 & Mount Joy Road……………………………….......52
Table 60. Time of day of crash at Delaware 30 & Mount Joy Road…………………………….53
Table 61. Period of day of crashes at Delaware 30 & Mount Joy Road…………………………54
Table 62. Day of week of crashes on Delaware 30 & Mount Joy Road…………………………54
Table 63. Month of crashes at Delaware 30 & Mount Joy Road………………………………...54
Table 64. Age of drivers responsible for crashes at Delaware 30 & Mount Joy Road…………..55
Table 65. Age of all drivers involved in crashes at Delaware 30 & Mount Joy Road…………..55
Table 66. Weather conditions during crashes at Delaware 30 & Mount Joy Road……………...56
Table 67. Road conditions during crashes at Delaware 30 & Mount Joy Road…………………56
Table 68. Alcohol related crashes at Delaware 30 & Mount Joy Road………………………….56
Table 69. Conversion to all way stop control at Delaware 30 & Mount Joy Road…………...…57
Table 70. Monetary value of crash reduction due to conversion to an all way stop at
Delaware 30 & Mount Joy Road……………………………………………………………...…58
Table 71. Cost to benefit ratio of converting Delaware 30 & Mount Joy Road
to a four way stop………………………………………………………………………………...59
Table 72. Types of crash summary at Delaware 30 & Zoar Road…………………………….…61
Table 73. Reason for crash summary at Delaware 30 & Zoar Road…………………………….62
Table 74. Approach of drivers responsible for crashes on Delaware 30 & Zoar Road………….62
Table 75. Crash severity at Delaware 30 & Zoar Road………………………………………….63
Table 76. Time of day of crashes at Delaware 30 & Zoar Road………………………………...63
Table 77. Period of day of crashes at Delaware 30 & Zoar Road……………………………….64
Table 78. Day of week of crashes at Delaware 30 & Zoar Road……………………………...…64
Table 79. Month of year of crashes at Delaware 30 & Zoar Road…………………………...….65
Table 80. Age of drivers responsible for crashes at Delaware 30 & Zoar Road………………...65
Table 81. Age of all drivers involved in crashes at Delaware 30 & Zoar Road………………....66
Table 82. Weather during crashes at Delaware 30 & Zoar Road………………………………..66
Table 83. Road conditions during crashes at Delaware 30 & Zoar Road……………………..…66
Table 84. Alcohol related crashes at Delaware 30 & Zoar Road……………………………...…67
Table 85. Conversion to all way stop control at Delaware 30 & Zoar Road………………….…68
Table 86. Highway Safety Manual crash modification factors
for overhead flashing beacons…………………………………………………………………...69
Table 87. Monetary value of crash reduction due to conversion to an all way stop at
Delaware 30 & Zoar Road……………………………………………………………………….70
Table 88. Cost to benefit ratio for converting Delaware 30 & Zoar Road to a four way stop…..70
1
1. Abstract
Delaware Department of Transportation (DelDOT) has identified five unsignalized
intersections in rural areas of Delaware as locations with higher than average crash rates over the
past three years. These intersections are Delaware 10 & Delaware 15, Delaware 15 & Barratts
Chapel Road, Delaware 15 & Andrews Lake Road, Delaware 30 & Mount Joy Road, and
Delaware 30 & Zoar Road. While none of these intersections meet the requirements for
signalization, the purpose of this study is to identify countermeasures that can be used to improve
safety at these intersections. The methodology used in this study begins with identifying what
types of crashes are occurring at each intersection and why the crashes are occurring through
review and statistical analysis of crash reports as well as intersection site visits. Through
completing a comprehensive literature review of other studies of rural unsignalized intersection
and following the methods dictated in the American Association of State Highway and
Transportation Officials’ (AASHTO) Highway Safety Manual, countermeasures were identified
to address the unique safety concerns of each intersection. To compare the expected
effectiveness of each countermeasure, cost-benefit ratios were calculated for each
countermeasure based on the estimated construction cost for the countermeasure and the
projected crash reduction potential over ten years.
At Delaware 10 & Delaware 15, conversion to a roundabout was the primary option
analyzed because of the equal distribution of inadequate gap acceptance crashes at this location,
and because plans are already underway at DelDOT to convert this intersection to a roundabout.
At Delaware 15 & Barratts Chapel Road, conversion to a four-way stop, conversion to a
roundabout, and employing a lane narrowing concept to draw attention to the intersection and
reduce travel speeds were considered. Converting the intersection to a four-way stop was found
2
to have the greatest cost-benefit ratio. Delaware 15 & Andrews Lake Road experiences a large
proportion of crashes at night, so adding lighting to the intersection and realigning the
intersection to reduce the skew angle were suggested. Other low cost and less invasive options
including checking the retroreflectivity of signs and pavement markings could also be beneficial
at this intersection. It was determined that adding lighting to the intersection has a higher cost-
benefit ratio than realignment of the intersection. In February 2012, DelDOT converted
Delaware 30 & Mount Joy Road and Delaware 30 & Zoar Road to four-way stops. Since these
intersections had a problem with inadequate gap acceptance crashes, the analysis of these
intersections suggest that the four-way stop conversion will be beneficial. The goal for the
outcome of this report is to provide DelDOT with a clear comparison of potential options for
safety improvement at these intersections.
3
2. Introduction
This report is the result of a safety study of five intersections that were identified by
Delaware Department of Transportation (DelDOT) as locations which have experienced a higher
than average crash rate over the past three years. The intersections are Delaware 10 & Delaware
15, Delaware 15 & Barratts Chapel Road, Delaware 15 & Andrews Lake Road, Delaware 30 &
Mount Joy Road, and Delaware 30 & Zoar Road. See Figure 1 below for the locations of these
intersections in Delaware.
Figure 1. Intersection locations
All of these intersections are rural, non-signalized intersections that do not meet the
requirements for signalization. The first three intersections, Delaware 10 & Delaware 15,
Delaware 15 & Barratts Chapel Road, and Delaware 15 & Andrews Lake Road are located in
Kent County. Delaware 30 & Mount Joy Road and Delaware 30 & Zoar Road are located in
4
Sussex County. The purpose of this study is to identify the factors that are causing crashes and
recommend countermeasures that can be used to reduce the crash rate at these intersections.
5
3. Project Overview and Methodology
The first step in this study is to determine the cause for the increased crash frequency at
each of the intersections which can be accomplished through visiting the site, reviewing crash
reports, and studying literature publications. Visiting the site of each intersection is an important
early step in the process to observe what conditions drivers experience at the intersection. The
Highway Safety Manual served as guidance for conducting site visits. As part of collecting data
about each intersection, the intersection was traversed from each direction and the experience
was compared with crash trends for the intersection. For example, sight distance from each
approach to the intersection was noted and objects that obscure the view of the oncoming traffic
were identified. Another factor to observe when performing a site visit to the intersection was
any advanced warning of the intersection and visibility when approaching the intersection.
Advanced warning of intersections can consist of signs, pavement markings, rumble strips, or
flashing beacons. It is necessary to note the advanced warning measures located on both the main
road and the cross road. Gap acceptance can be a challenge at rural, non-signalized intersections
if the volume on the main road is large enough. When performing a site visit, the driver can see
first-hand what ordinary drivers must contend with in order to find an acceptable gap. If
acceptable gaps are infrequent, this could cause drivers to become impatient and decide to enter
the intersection when conditions are not safe. Observing driver behavior at the intersection can
provide valuable insight to driving trends at a particular location. An observer can look at the
travel speed of the vehicles in comparison to the posted speed limit, the queue of vehicles that
backup at a stop sign, or any other notable driver behavior factors.
Crash reports from each of the five intersections where provided from DelDOT for three
years prior to the study. These reports reveal vital data in determining the reason for crashes.
6
From the crash reports, information regarding the type of crash, time of the crash, reason for
crash, weather conditions, and severity of crash can be analyzed. Through this information,
trends are examined. The time of the day, the week of the month, and the month of the year of
the crashes can be searched for patterns. The crash reports also list the birthdate of the drivers
involved in the crash, so the ages of the drivers involved can be calculated. The reason for a
crash can be determined from the crash report through the crash narrative. If the drivers are
unable or unwilling to describe to the police officer who produced the crash report, information
about which direction the vehicles in the crash were travelling is still available and can be used
to make educated assertions about the cause of the crash. It is also useful to draw a crash diagram
using the instruction in the Highway Safety Manual to get a visual representation of where the
crashes typically occur at the intersection. The data collected from the crash reports was
organized into tables and graphs that highlight common trends at each intersection.
Once the causes of the crashes at each intersection are determined through gathering and
analyzing the data, countermeasures must be identified to mediate the problems occurring at the
intersections. For this step it is vital to review literature and other published studies to determine
what countermeasures can be used for each type of problem experienced at the intersections.
While one countermeasure may be very effective at one intersection, if the conditions are
different at another intersection or the reason for crash is different, the same countermeasure may
not result in the same level of success. The literature reviewed for this project includes studies
from sources such as the US Department of Transportation Federal Highway Administration,
Kansas State University, Texas Department of Transportation, Minnesota Department of
Transportation, the Highway Safety Manual, and the Washington State Department of
Transportation.
7
After potential countermeasures were selected, calculations were done to estimate the
effectiveness of the countermeasures in terms of predicted yearly crash reduction. These
calculations were performed using the predictive method and crash modification factors (CMFs)
listed in the Highway Safety Manual. The final step of the study was to calculate the cost for
each proposed improvements and determine a cost-benefit ratio from the previously determined
crash reduction values to evaluate the alternatives. In calculating the expected benefits of a
countermeasure, the Highway Safety Manual has determined that the cost to society of a
property damage only crash is $7,400 and the cost of a fatality/ injury crash is $158,200. The
benefits of the countermeasure were calculated over a period of 10 years using the expected
crash reduction for each countermeasure and with an assumed discount rate of 4%. In order to
determine the present value of the annual series of expected benefits Equation 1 was used where
i represents the discount rate
Equation 1
8
4. Delaware 10 & Delaware 15
Figure 2. Delaware 10 and Delaware 15 location map
4.1 Site Overview and Site Visit Observations
Delaware 10 & Delaware 15 is a four way intersection located in Kent County south of
Dover. Delaware 10 runs eastbound and westbound in the vicinity of the intersection and is
named Willow Grove Road at this location. The northbound approach to the intersection on
Delaware 15 is known as Dundee Road, and the southbound approach to the intersection on
Delaware 15 is referred to as Moose Lodge Road. The major road is Delaware 10 which has an
average annual daily traffic (AADT) value of 5,062 vehicles per day. Delaware 15 is stop
controlled at the intersection and has an AADT value of 2,634 vehicles per day. The speed limit
on Delaware 10 in the vicinity of the intersection is 50 miles per hour, and the speed limit on
9
Delaware 15 is 35 miles per hour. In the past three years, 25 crashes have occurred at this
intersection.
The site visit revealed that the volume of traffic on Delaware 10 is relatively fast moving
and heavy which makes it difficult for drivers to safely cross the intersection. A short queue
frequently builds up in the northbound and southbound approaches even at off peak hours due to
drivers waiting to cross the intersection. The sight distance is limited from the southbound
approach due to trees and signs to the left, and the sight distance is also obstructed from the
northbound approach due to a silver utility box. The intersection appears roughly at grade with
minimal horizontal curvature in the vicinity of the intersection. Lighting is installed at the
intersection. Advanced warning for the intersection includes “STOP AHEAD” signs and
pavement markings from the northbound and southbound approaches. The only warning of the
approaching intersection from the eastbound and westbound approaches is a sign with the
upcoming road names. There is one lane in each direction for all approaches. The eastbound and
westbound approaches to the intersection have paved shoulders, but the northbound and
southbound approaches do not have a paved shoulder.
4.2 Intersection Trends and Reasons for Crash Analysis
The most common reason for crashes at Delaware 10 & Delaware 15 is drivers on a
minor road approach who have difficulty selecting a safe gap in traffic when crossing the
intersection, but rear end collisions are also common. Table 1 below shows the most common
types of crashes at Delaware 10 & Delaware 15.
10
Table 1. Types of crash at Delaware 10 & Delaware 15
Type of Crash Frequency Percentage
Failure to remain stopped 13 52%
Rear end collision 5 20%
Ran stop sign 3 12%
Failure to yield right of way 2 8%
Deer in roadway 1 4%
Improper passing on right 1 4%
The most common reasons for crashes cited by drivers at Delaware 10 & Delaware 15
were drivers who did approach the intersection from the northbound or southbound approaches
and did not see the cross traffic or inattentive driving. Since the volume of traffic on Delaware 10
is high, inattentive drivers are likely to misjudge the amount of time needed to cross the
intersection. See Table 2 below for a summary of the reasons for crashes at Delaware 10 &
Delaware 15.
Table 2. Reason for crash summary at Delaware 10 & Delaware 15
Reason for Crash Frequency Percentage
Didn’t see vehicle WB: 5 WB: 20%
EB: 5 EB: 20%
Inattentive driving 8 32%
DUI 2 8%
Unknown 2 8%
Roadway conditions 1 4%
Vehicle blocking view 1 4%
Driver confusion 1 4%
Table 3 shows a summary of the approach direction of drivers responsible for crashes.
This information could identify significant issues with an approach to the intersection such as
sight distance problems if a majority of crashes occurred from a specific approach. In the case of
Delaware 10 & Delaware 15, a nearly equal amount of crashes occurred from the northbound
11
and southbound approach which suggests that there is not a particular problem at one approach
to the intersection.
Table 3. Approach of driver responsible for crash at Delaware 10 & Delaware 15
Approach Frequency Percentage
Northbound 9 36%
Southbound 10 40%
Eastbound 5 20%
Westbound 1 4%
Table 4 below shows that more than half of the crashes occurring at the intersection of
Delaware 10 & Delaware 15 are personal injury crashes. This is likely due to the fact that the
speed limit on Delaware 10 is 50 mph so the traffic is moving quickly at the intersection and the
majority of the crashes at the intersection are due to a collision of a vehicle entering the
intersection from a minor road approach colliding with a vehicle on Delaware 10.
Table 4. Crash severity summary at Delaware 10 & Delaware 15
Severity Frequency Percentage
Property Damage Only 9 36%
Personal Injury 16 64%
Table 5 shows that crashes at Delaware 10 & Delaware 15 are occurring mainly during
the daytime with higher rates during the traditional morning and afternoon peak hour periods.
12
Table 5. Time of day of crash summary at Delaware 10 & Delaware 15
Hour of Day Number Of Crashes Percentage
0:00-1:00 1 4%
1:00-2:00
2:00-3:00
3:00-4:00
4:00-5:00
5:00-6:00
6:00-7:00
7:00-8:00 2 8%
8:00-9:00
9:00-10:00 1 4%
10:00-11:00 3 12%
11:00-12:00 1 4%
12:00-13:00 1 4%
13:00-14:00 2 8%
14:00-15:00 2 8%
15:00-16:00 4 16%
16:00-17:00
17:00-18:00 4 16%
18:00-19:00 1 4%
19:00-20:00
20:00-21:00 1 4%
21:00-22:00 1 4%
22:00-23:00 1 4%
23:00-24:00
Table 6 supports Table 5 in showing that the majority of the crashes at Delaware 10 &
Delaware 15 occurred during the day.
Table 6. Period of day of crashes at Delaware 10 & Delaware 15
Time of Day Number of Crashes Percentage
Day 18 72%
Night 5 20%
Dusk 2 8%
13
Table 7 below shows that the highest number of crashes at this intersection occurred on
Tuesday; however, the crashes appear to be roughly evenly distributed across all days of the
week.
Table 7. Day of week of crashes at Delaware 10 & Delaware 15
Day of Week Number of Crashes Percentage
Sunday 2 8%
Monday 3 12%
Tuesday 6 24%
Wednesday 2 8%
Thursday 5 20%
Friday 4 16%
Saturday 3 12%
Table 8 below shows that the months with the highest crash rate are June and August, but
does not suggest any seasonal crash trends.
Table 8. Month of crash summary at Delaware 10 & Delaware 15
Month of the Year Number of Crashes Percentage
January 2 8%
February 3 12%
March 3 12%
April 2 8%
May 2 8%
June 4 16%
July 1 4%
August 4 16%
September 1 4%
October
November 2 8%
December 1 4%
Table 9 shows that younger drivers below the age of 30 are responsible for half of the
crashes that occur at the intersection of Delaware 10 & Delaware 15. While this does appear to
14
be a significant trend, it is not specific to this intersection. Younger drivers are typically more
inexperienced than older drivers and frequently have a higher crash rate than more experienced
drivers. Elderly drivers do not appear to be causing a significant number of crashes at this
intersection.
Table 9. Age of drivers responsible for crash at Delaware 10 & Delaware 15
Age Number of Crashes Percentage
16-19 6 25%
20-29 6 25%
30-39 2 8.33%
40-49 4 16.67%
50-59 3 12.5%
60-69 2 8.33%
70 and older 1 4.17%
Table 10 shows the ages of all people involved in the crashes. A higher proportion of the
people involved in crashes are middle aged than are causing the crashes.
Table 10. Age of all drivers involved in crashes at Delaware 10 & Delaware 15
Age Number of Crashes Percentage
16-19 7 13.73%
20-29 13 25.49%
30-39 5 9.80%
40-49 9 1.76%
50-59 10 19.61%
60-69 5 9.80%
70 and older 1 1.96%
Unknown 1 1.96%
Table 11 demonstrates that the majority of the crashes occurred when the weather was
clear.
15
Table 11. Weather conditions during crashes at Delaware 10 & Delaware 15
Weather Number of Crashes Percentage
Rainy 3 12%
Cloudy 3 12%
Clear 19 76%
Table 12 shows that while a few of the crashes did occur when the roads were wet, road
conditions do not appear to be a significant contributing factor to the cause of crash.
Table 12. Road conditions during crashes at Delaware 10 & Delaware 15
Road Condition Number of Crashes Percentage
Dry 20 80%
Wet 5 20%
Table 13 shows that two crashes were attributed to alcohol impairment at Delaware 10 &
Delaware 15.
Table 13. Alcohol related crashes at Delaware 10 & Delaware 15
Number of Crashes Percentage
Alcohol Related 2 8%
Not Alcohol Related 23 92%
From the site visit and review of the crash reports at Delaware 10 & Delaware 15, it is
suggested that gap acceptance problems resulting from the relatively heavy volume on both
roads and due to inattentive driving and limited sight distance are the primary cause for crashes
at the intersection.
16
4.3 Suggested Countermeasures and Projected Effectiveness
DelDOT has proposed that the intersection of Delaware 10 & Delaware 15 be converted
to a roundabout. Roundabouts are known to have a much lower crash rate than stop controlled
intersections. In the case of Delaware 10 & Delaware 15, crashes are evenly distributed from
both minor road approaches which supports the judgment that the volume and speed of traffic on
Delaware 10 is one of the primary causes of inadequate gap acceptance crashes instead of poor
roadway geometrics or sight distance at one approach. For a roundabout to be most effective, the
traffic on both roads at the intersection should have similar volumes. While Delaware 10 has a
greater volume than Delaware 15, Delaware 15 still has a significant volume given the rural
location which should allow a roundabout at this location to function properly and achieve the
desired safety improvements. According to the predictive method cited by the Highway Safety
Manual, converting an intersection with minor road stop control into a rural, one lane roundabout
has a CMF of 0.29 with a standard deviation of 0.04 for all crashes, and a CMF of 0.13 with a
standard deviation of 0.01 for injury crashes. The main obstacles facing the roundabout
conversion include public opposition to roundabouts because they are uncommon in the area,
cost for construction, and expanded right-of-way needed. See Table 14 below for the expected
crash reduction due to converting the intersection to a roundabout.
Table 14. Crash reduction due to roundabout conversion at Delaware 10 & Delaware 15
Expected crashes per year with
no treatment
Expected crashes per year with
roundabout conversion (95%
confidence interval)
All Crashes 8.33 2.42 (1.75-3.08)
Injury 5.33 0.69 (0.59-0.80)
17
4.4 Cost/ Benefit Analysis
Converting an intersection into a roundabout is an expensive and time consuming
process, but the crash reduction potential is significant. Table 15 below shows the calculations of
the expected monetary benefit to society per year from injury reduction resulting from
converting the intersection to a roundabout.
Table 15. Monetary value of crash reduction for roundabout conversion at Delaware 15 &
Delaware 10
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
5.33 4.64 $734,048
Property Damage
Only Crashes
3.33 1.27 $9,398
TOTAL $743,446
When applying the benefits over ten years using Equation 1, the expected benefit is
calculated to be $6,030,013.
The cost to convert a non-signalized intersection into a rural, one lane roundabout ranges
from $200,000-$1,000,000. Since roundabouts require a greater amount of land than a typical
four way intersection, it may be necessary to acquire additional right-of-way. If the center of the
roundabout is landscaped it may require some yearly maintenance, but it is expected that a
roundabout will have minimal maintenance costs over the first ten years following the
construction. Therefore, the cost of the roundabout over ten years includes only the initial cost.
See Table 16 for a summary of the monetary costs and benefits over ten years of converting
Delaware 10 & Delaware 15 into a roundabout.
18
Table 16. Cost benefit analysis for roundabout at Delaware 10 & Delaware 15
Countermeasure Cost Benefits Cost: Benefit
Ratio (Lower
bound)
Cost: Benefit
Ratio (Upper
Bound)
Conversion to
roundabout
$200,000-
$1,000,000
$6,030,013 1:6.0 1:30.2
As Table 16 shows, the benefits of converting Delaware 10 & Delaware 15 into a
roundabout is expected to reap benefits of 6-12 times the initial cost of construction over a ten
year period due to crash reduction.
19
5. Delaware 15 & Barratts Chapel Road
Figure 3. Delaware 15 and Barratts Chapel Road location map
5.1 Site Overview and Site Visit Observations
Delaware 15 & Barratts Chapel Road is located outside of Riverview, Delaware in Kent
County. Delaware 15 is known as Canterbury Road in the vicinity of the intersection and runs in
the north and south directions. Barratts Chapel Road is the westbound approach to the
intersection, and the eastbound approach to the intersection is called Plymouth Road. Barratts
Chapel Road and Plymouth Road have stop signs at the intersection with Delaware 15, but traffic
on Delaware 15 does not stop at the intersection. The AADT on Delaware 15 is 4,333 vehicles
per day, and the AADT on Barratts Chapel Road is 1,447 vehicles per day. The posted speed
limit on the northbound and southbound approaches is 40 miles per hour, and the posted speed
20
limit on the eastbound and westbound approaches is 35 miles per hour. There have been fifteen
crashes at the intersection of Delaware 15 & Barratts Chapel Road over the past three years.
The intersection site visit revealed that sight distance from the eastbound and westbound
approaches are less than ideal. Although the intersection is not lighted, there are flashing lights
near the intersection. From the eastbound and westbound approaches, there are “STOP AHEAD”
signs with yellow flashing lights and “STOP AHEAD” pavement markings as well as red
flashing lights on the stop signs. From the northbound and southbound directions, there are
intersection warning signs with red flashing lights. All approaches to the intersection are one
lane in each direction with no turning lanes. Due to the relatively large volume of traffic on
Delaware 15, finding an acceptable gap to cross or turn onto Delaware 15 proved difficult.
5.2 Intersection Trends and Reasons for Crash Analysis
The most common type of crash at Delaware 15 & Barratts Chapel Road was the result of
drivers stopped on the northbound or southbound approach stop signs who fail to wait for the
cross traffic to clear before moving into the intersection. As Table 17 below indicates, the type of
crashes at Delaware 15 & Barratts Chapel Road are diverse.
Table 17. Type of crash summary for Delaware 15 & Barratts Chapel Road
Type of Crash Frequency Percentage
Failure to remain stopped 5 33.3%
Ran off road 2 13.3%
Driving on wrong side of road 2 13.3%
Ran stop sign 1 6.7%
Failure to yield right of way 1 6.7%
Illegally parked vehicle 1 6.7%
Careless driving 1 6.7%
Improper turn 1 6.7%
Unknown 1 6.7%
21
Table 18 shows the reasons for crash at Delaware 15 & Barratts Chapel Road. The most
common reasons for crash are drivers who did not see the cross traffic which is in line with the
most common crash type being failure to remain stopped at the stop sign. Similarly to Table 17,
the reason for crashes is diverse with a considerable number of crashes with unknown causes.
Table 18. Reason for crash summary at Delaware 15 & Barratts Chapel Road
Reason for Crash Frequency Percentage
Didn’t see vehicle NB: 2 13.3%
SB: 2 13.3%
Driver thought gap was
acceptable
1 6.7%
DUI 1 6.7%
Unfamiliar with road 1 6.7%
Dark 1 6.7%
Wet road 1 6.7%
Driver fell asleep 1 6.7%
Expected four way stop 1 6.7%
Unknown 4 26.7%
Table 19 below shows a summary of the approach direction of vehicles responsible for
crashes. Nearly half of the crashes at this intersection occurred from the westbound approach.
The number of crashes from the westbound approach is more than double the crashes from any
of the other approaches. This data suggests that there may be a problem with the westbound
approach to the intersection which is causing safety problems.
Table 19. Approach of driver responsible for crash at Delaware 15 & Barratts Chapel Road
Direction Frequency Percentage
NB 2 13.3%
SB 3 20%
EB 3 20%
WB 7 46.7%
22
Table 20 shows the severity of crashes at Delaware 15 & Barratts Chapel Road. More
than half of the crashes resulted in only property damage.
Table 20. Crash severity summary at Delaware 15 & Barratts Chapel Road
Severity Frequency Percentage
Property Damage Only 11 73.3%
Personal Injury 4 26.7%
Table 21 shows the distribution of the crashes over the hours of the day. A majority of the
crashes occur during the afternoon, but this table does not appear to demonstrate any unexpected
pattern.
Table 21. Time of day of crashes at Delaware 15 & Barratts Chapel Road
Time Number Of Crashes Percentage
0:00-1:00 1 6.67%
1:00-2:00
2:00-3:00
3:00-4:00
4:00-5:00
5:00-6:00 1 6.67%
6:00-7:00 2 13.33%
7:00-8:00
8:00-9:00
9:00-10:00 1 6.67%
10:00-11:00
11:00-12:00
12:00-13:00
13:00-14:00 2 13.33%
14:00-15:00 2 13.33%
15:00-16:00 1 6.67%
16:00-17:00 1 6.67%
17:00-18:00
18:00-19:00 2 13.33%
19:00-20:00
20:00-21:00
21:00-22:00 2 13.33%
22:00-23:00
23:00-24:00
23
Table 22 below shows that most of the crashes at Delaware 15 & Barratts Chapel Road
occur during the day when the sun is out. This intersection is not lighted, so it could explain why
over one quarter of the crashes occur during the night. The flashing beacons on the stop signs
and intersection warning signs could help with night visibility. Table 22 indicates a slight
problem with nighttime visibility at the intersection.
Table 22. Period of day of crashes at Delaware 15 & Barratts Chapel Road
Time of Day Number of Crashes Percentage
Day 9 60%
Night 4 26.67%
Dawn 2 13.33%
When examining the day of the week of crashes occurring at Delaware 15 & Barratts
Chapel Road, it was discovered that 40% of the crashes occurred on Saturdays. This trend could
be the result of land uses nearby. It is possible that there may be an event on Saturdays that
attracts more traffic to the area and increased the crash rate as a result. See Table 23 below for a
summary of the distribution of crashes at Delaware 15 & Barratts Chapel Road over the days of
the week.
Table 23. Day of the week of crashes at Delaware 15 & Barratts Chapel Road
Day of Week Number of Crashes Percentage
Sunday 1 6.67%
Monday 0 0%
Tuesday 2 13.33%
Wednesday 3 20%
Thursday 2 13.33%
Friday 1 6.67%
Saturday 6 40%
24
As shown in Table 24, the month with the greatest number of crashes at Delaware 15 &
Barratts Chapel Road is January; however, it does not appear that there are noticeably more
crashes during any one period of the year to suggest a trend.
Table 24. Month of year of crashes at Delaware 15 & Barratts Chapel Road
Month of the Year Number of Crashes Percentage
January 4 26.67%
February 1 6.67%
March 1 6.67%
April 1 6.67%
May 2 13.33%
June 1 6.67%
July 2 13.33%
August
September
October 1 6.67%
November
December 2 13.33%
Table 25 shows the ages of the drivers responsible for crashes at Delaware 15 & Barratts
Chapel Road. The age group with the greatest number of crashes is under 20. This trend is
consistent with the expected tendency for younger drivers to have a higher crash rate than other
drivers.
Table 25. Age of drivers responsible for crash at Delaware 15 & Barratts Chapel Road
Age Number of Crashes Percentage
16-19 3 20%
20-29 2 13.33%
30-39 2 13.33%
40-49 2 13.33%
50-59 1 6.67%
60-69 1 6.67%
70 and older 1 6.67%
Unknown 3 20%
25
Table 26 shows that the age of all drivers involved in crashes at Delaware 15 & Barratts
Chapel Road is roughly evenly distributed.
Table 26. Ages of all drivers involved in crashes at Delaware 15 & Barratts Chapel Road
Age Number of Crashes Percentage
16-19 3 10.34%
20-29 4 13.80%
30-39 3 10.34%
40-49 5 17.24%
50-59 5 17.24%
60-69 4 13.80%
70 and older 2 6.90%
Unknown 3 10.34%
As shown in Table 27, the majority of the crashes at Delaware 15 & Barratts Chapel
Road occurred when the weather was clear.
Table 27. Weather conditions during crashes at Delaware 15 & Barratts Chapel Road
Weather Number of Crashes Percentage
Clear 11 73.33%
Cloudy 1 6.67%
Rainy 2 13.33%
Unknown 1 6.67%
Table 28 shows the road conditions during crashes at Delaware 15 & Barratts Chapel
Road. It does not appear that adverse road conditions greatly contributed to the frequency of
crashes at this location.
Table 28. Road conditions during crashes at Delaware 15 & Barratts Chapel Road
Road Condition Number of Crashes Percentage
Wet 3 20%
Dry 11 73.33%
Unknown 1 6.67%
26
As shown in Table 29, one crash at Delaware 15 & Barratts Chapel Road was caused by
an impaired driver which does not suggest a significant problem.
Table 29. Alcohol related crashes at Delaware 15 & Barratts Chapel Road
Number of Crashes Percentage
Alcohol Related 1 6.67%
Not Alcohol Related 14 93.33%
5.3 Suggested Countermeasures and Projected Effectiveness
One option considered for improving the safety of Delaware 15 & Barratts Chapel Road
is changing the intersection from minor road stop controlled to all way stop controlled. This
countermeasure was considered because drivers on the minor road approach are having difficulty
judging when it is safe to enter the intersection. While stopping traffic on Delaware 15 at this
intersection would delay traffic and could increase the number of rear-end collisions at the major
road approach, the four-way stop would allow traffic on Barratts Chapel Road to have an easier
and safer chance to turn or cross this intersection. Drivers travelling southbound on Delaware 15
pass through an all way stop controlled intersection shortly before reaching the intersection with
Barratts Chapel Road, so these vehicles are likely travelling more slowly and could easily adapt
to another stop sign at Barratts Chapel Road. The MUTCD has outlined specific guidelines for
the warranting of multi-way stop that were consulted when considering the option of converting
this intersection into a four way stop. Qualification B states that a multi-way stop is warranted if
more than five crashes that could be prevented by a multi-way stop occur in a twelve month
period. This intersection averages three crashes per year that could be corrected with a multi-way
stop sign including four such crashes in 2010 alone. Qualification C states that a multi-way stop
is warranted if the traffic on the major road exceeds 300 vehicles per hour and the traffic on the
27
minor road exceeds 200 vehicles per hour for more than eight hours. If the 85th percentile speed
is greater than 40 mph on the major road, the volume requirements can be decreased by 30%.
Qualification D states that if qualifications B and C are completed to 80%, then a multi-way stop
is warranted. According to the predictive method in the Highway Safety Manual, if an
intersection meets the requirements in the MUTCD for conversion to a multi-way stop has a
crash modification factor of 0.52 with a standard error of 0.04. See Table 30 below for the
expected number of crashes if the intersection were converted to an all way stop.
Table 30. Expected crash reduction for conversion to all way stop control at Delaware 15 &
Barratts Chapel Road
Expected crashes per year
with no treatment
Expected crashes per year
with all-way STOP conversion
All Crashes 5 2.60 (2.40-2.80)
A second way crashes could potentially be reduced at this intersection would be through
increasing the sight distance from the westbound approach. The crash reports show that there are
more crashes occurring from the westbound approach than the eastbound approach, so it
indicates that there may be a problem with the visibility. This problem could be mitigated
through increasing the sight distance.
A third option for improving the safety of this intersection would be converting it to a
roundabout. One of the main advantages of roundabouts are their ability to mitigate gap
acceptance problems at intersections. Since the biggest cause of crashes at Delaware 15 &
Barratts Chapel Road is drivers who fail to remain stopped at the minor road approach stop
signs, it would be a good candidate to consider for roundabout conversion. As mentioned in the
previous section, the crash reduction factor as identified by the Highway Safety Manual for
28
roundabouts is 0.29 with a standard deviation of 0.04 for all crashes and 0.13 with a standard
deviation of 0.01 for injury crashes. See Table 31 below for the expected crash reduction if
Delaware 15 & Barratts Chapel Road were converted to a roundabout.
Table 31. Expected crash reduction for conversion to roundabout at Delaware 15 & Barratts
Chapel Road
Expected crashes per year with
no treatment
Expected crashes per year with
roundabout conversion (95%
confidence interval)
All Crashes 5 1.45 (1.05-1.85)
Injury 1.33 0.17 (0.15-0.20)
A final suggestion for altering Delaware 15 & Barratts Chapel Road to improve safety
would be to employ a lane narrowing concept designed to reduce travel speed at the intersection
and draw greater attention to the intersection from the minor road approach. Traffic travelling
north on Delaware 15 has a 50 mph speed limit until shortly before the intersection with Barratts
Chapel Road. Vehicles that do not reduce their speeds to conform to the reduced speed limit are
a hazard to vehicles on Barratts Chapel Road trying to turn onto or cross Delaware 15.
Narrowing the lanes on a road is frequently used to reduce travel speeds, so this type of
countermeasure could be particularly effective since the average vehicle speed on Delaware 15 is
believed to be greater than the posted speed limit at this location. A study done by the Federal
Highway Administration identified two possible configurations of lane narrowing at intersections
as well as a combination of the two methods. The first method is to reduce the lane width on the
major road to 9-10 feet through installing a painted median lined with rumble strips as shown in
Figure 4. The purpose of reducing the lane width is to force drivers to slow down at the
intersection. By creating a painted median with rumble strips, the drivers do not have the added
29
hazard of a raised median that could potentially increase the crash rate. The use of a painted
median also decreases project cost and construction time.
Figure 4. Lane narrowing concept one (Source: Federal Highway Administration)
When installed at an intersection, the first lane narrowing concept would appear to
drivers as shown in Figure 5.
Figure 5. Field view of lane narrowing concept one (Source: Federal Highway Administration)
30
The second lane narrowing concept, shown in Figure 6, involves creating a channelizing
separator island on the minor road approach and adding an extra stop sign on the new median to
draw more attention to the intersection from the minor road approach. This measure would
increase intersection awareness and improve driver alertness.
Figure 6. Lane narrowing concept two (Source: Federal Highway Administration)
In the field, the second lane narrowing concept would look like Figure 7.
Figure 7. Field view of lane narrowing concept two (Source: Federal Highway Administration)
31
The final option for intersection lane narrowing identified by the Federal Highway
Administration study involves combining the two previous shown concepts into one design as
shown in Figure 8. This third option combines both the modifications to the intersection from the
major road and minor road approaches to maximize speed reduction and intersection awareness.
Figure 8. Combined lane narrowing concept (Source: Federal Highway Administration)
The study of the effectiveness of the lane narrowing concept at reducing speed was done
using nine sites in Pennsylvania, Kentucky, Missouri, and Florida. The study revealed
statistically significant results at a 95th percentile confidence interval for reduction of speed on
the major road through the implementation of lane narrowing concept one.
A study of the effect of lane narrowing concept one on crash reduction showed mixed,
but generally positive results. For the three sites in Pennsylvania, total crashes were reduced
between 30% and 83%. Fatal crashes and related crashes were also reduced at all Pennsylvania
32
sites. However, the sites in Kentucky, Missouri, and Florida observed an increase in rear-end
collisions. Overall, the sites experienced a 31% decrease in total crashes and a 20% decrease in
fatal/injury crashes.
Only one site in Virginia was studied for lane narrowing concept two on the minor road.
This location experienced a decrease in both angle and rear-end collisions. Total crashes at this
site decreased by 68% and fatal/ injury crashes decreased by 74%.
While the number of trials in the sample of the Federal Highway Administration study is
limited, the outcomes can still be used to estimate the crash decrease expected if lane narrowing
concept one were implemented at Delaware 15 & Barratts Chapel Road. The Highway Safety
Manual does not provide specific crash modification factors for this countermeasure treatment.
See Table 32 for an estimation of the crash reduction at Delaware 15 & Barratts Chapel Road
using the crash reduction values from the study of the nine sites used in the Federal Highway
Administration study.
Table 32. Expected crash reduction for lane narrowing concept at Delaware 15 & Barratts
Chapel Road
Expected crashes per year with
no treatment
Expected crashes per year with
roundabout conversion
All Crashes 5 3.45
Injury 1.33 1.06
See the Federal Highway Administration publication “Two Low-Cost Safety Concepts
for Two-Way STOP-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way
Roadways” cited in the references for more information regarding the study of the lane
narrowing concepts.
33
5.4 Cost/ Benefit Analysis
As demonstrated in the previous section, changing Delaware 15 & Barratts Chapel Road
to an all way stop, the crash rate is expected to decrease. Table 33 below summarizes the
calculations made to determine the monetary benefits to society for the expected crash reduction
due to converting Delaware 15 & Barratts Chapel Road into an all way stop.
Table 33. Monetary value of crash reduction for all way stop conversion at Delaware 15 &
Barratts Chapel Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
1.33 0.64 $101,248
Property Damage
Only Crashes
3.67 1.76 $13,024
TOTAL $114,272
Using Equation 1, the present value of the expected monetary benefit over ten years from
crash reduction due to converting Delaware 15 & Barratts Chapel Road into an all way stop is
$926,848.
Table 34 below summarizes the calculations for the monetary value of crash reduction
projected to result from converting Delaware 15 & Barratts Chapel Road into a rural, one lane
roundabout.
34
Table 34. Monetary value of crash reduction for conversion to a roundabout at Delaware 15 &
Barratts Chapel Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
1.33 1.16 $183,512
Property Damage
Only Crashes
3.67 2.39 $17,686
TOTAL $201,198
Using Equation 1 to calculate the present value of the crash reduction due to roundabout
conversion over ten years, the benefit is $1,631,896.
Table 35 summarizes the calculations for the estimated monetary value of crash reduction
due to using the lane narrowing concept at Delaware 15 & Barratts Chapel Road.
Table 35. Expected monetary value of crash reduction for lane narrowing concept at Delaware
15 & Barratts Chapel Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
1.33 0.27 $42,714
Property Damage
Only Crashes
3.67 1.76 $9,472
TOTAL $52,186
The projected present value of the benefits from crash reduction using the lane narrowing
concept at Delaware 15 & Barratts Chapel Road as calculated from Equation 1 are $423,275.
As explained in the previous section, the cost of converting a rural intersection to a
roundabout typically ranges from $200,000 to $1,000,000. Improving the sign and marking at the
intersection to convert the intersection from a two-way stop into a four-way stop is estimated to
35
cost between $100 and $1,000. The intersection lane narrowing concept would require milling to
remove the current pavement markings, rumble strips added to create the median, and new line
painting. For the intersections in the study where this treatment was applied, the cost of
installation ranged between $10,000 and $70,000. See Table 36 below comparing the cost to
benefit ratios for the three suggested countermeasures at Delaware 15 & Barratts Chapel Road.
Table 36. Cost to benefit ratio for proposed Delaware 15 & Barratts Chapel countermeasures
Countermeasure Cost Benefits Cost: Benefit
Ratio (lower
bound)
Cost: Benefit
Ratio (upper
bound)
Conversion to
roundabout
$200,000-
$1,000,000
$1,631,896 1:1.6 1:8.2
Conversion to
four-way stop
$100-$1,000 $926,848 1:926.9 1:9268.5
Intersection lane
narrowing
$10,000-
$70,000
$423,275 1:6.0 1:42.3
As shown by Table 36, the countermeasure with greatest cost to benefit ratio is
converting the intersection to a four way stop due to the very low cost of the countermeasure
relative to the other suggested treatments.
36
6. Delaware 15 & Andrews Lake Road
Figure 9. Delaware 15 and Andrews Lake Road location map
6.1. Site Overview and Site Visit Observations
The intersection of Delaware 15 & Andrews Lake Road is located outside of Riverview,
Delaware in Kent County. This intersection is located three tenths of a mile south of Delaware
15 & Barratts Chapel Road. Delaware 15 is still known as Canterbury Road in this area and
Andrews Lake Road is the name of the road from both the eastbound and westbound approaches
to the intersection. The AADT on Delaware 15 at this intersection is 4,300 vehicles per day, and
the AADT on Andrews Lake Road is 1,170. Andrews Lake Road has a stop sign at both the
eastbound and westbound approaches, but the traffic on Delaware 15 from the northbound and
southbound approaches does not stop. The posted speed limit on Delaware 15 is increased to 50
37
miles per hour at this intersection. Ten crashes have occurred at this intersection in the past three
years with six crashes occurring in 2010.
The site visit to Delaware 15 & Andrews Lake Road revealed many important
characteristics of the intersection. Andrews Lake Road does not form a 90 degree angle with
Delaware 15 at the intersection. It is difficult to see traffic travelling northbound from the
westbound approach due to the angle of intersection, and making a left turn from the westbound
direction is challenging due to the fact that the driver must turn greater than 90 degrees. Drivers
were observed making the left turn from the southbound approach at a relatively rapid speed due
to the angle of intersection which was cited as a common cause for crash at the intersection. All
approaches to the intersection are one lane in each direction and no approaches have a paved
shoulder. The intersection is not lighted which is an important fact to note when reviewing the
time of day for the crashes. The topography is reasonably flat near the intersection, and there is a
small horizontal curve from the northbound approach. “STOP AHEAD” signs are located from
the eastbound and westbound approaches. From the northbound and southbound approaches,
there is a sign designating the name of Andrews Lake Road.
6.2. Intersection Trends and Reasons for Crash Analysis
Table 37 below summarizes the type of crashes that occurred at Delaware 15 & Andrews
Lake Road. The most common types of crash were drivers on Andrews Lake Road who failed to
wait for a large enough break in traffic to cross the road and drivers on Delaware 15 who turned
in front of oncoming traffic.
38
Table 37. Type of crash at Delaware 15 & Andrews Lake Road
Type of Crash Frequency Percentage
Failure to remain stopped 4 40%
Failure to yield right of way 2 20%
Ran off road 1 10%
Improper turn 1 10%
Rear end collision 1 10%
Unknown 1 10%
As Table 38 shows, the cited reason for crashes at Delaware 15 & Andrews Lake Road
was most commonly the driver did not see cross traffic at the intersection, but frequently the
reason for the crash was unknown.
Table 38. Reason for crashes at Delaware 15 & Andrews Lake Road
Reason for Crash Frequency Percentage
Didn’t see vehicle SB: 2 SB: 20%
NB: 1 NB: 10%
Following too close 1 10%
DUI 1 10%
Unknown 5 50%
Table 39 shows that crashes are evenly distributed between the eastbound and westbound
minor road approaches. More crashes occurred from the southbound approach than the
northbound approach. Many of the crashes that occurred from the southbound approach were the
result of drivers making the turn onto Andrews Lake Road too quickly as a result of the roads not
intersecting at 90 degrees.
Table 39. Approach direction of vehicle responsible for crash at Delaware 15 & Andrews Lake
Road
Direction Frequency Percentage
NB 1 10%
SB 4 40%
EB 2 20%
WB 3 30%
39
As shown in Table 40, crash severity is evenly divided between crashes causing injury to
the people involved and crashes that only involve property damage.
Table 40. Crash severity at Delaware 15 & Andrews Lake Road
Severity Frequency Percentage
Property Damage Only 5 50%
Personal Injury 5 50%
Table 41 below shows the distribution of crashes at Delaware 15 & Andrews Lake Road
over the time of the day. The clustering of crash times does not follow the expected trend of
more crashes occurring during the traditional morning and afternoon peak hours when volume on
the roads are typically the greatest.
40
Table 41. Time of day of crashes at Delaware 15 & Andrews Lake Road
Time Number Of Crashes Percentage
0:00-1:00 1 10%
1:00-2:00 1 10%
2:00-3:00
3:00-4:00
4:00-5:00
5:00-6:00
6:00-7:00
7:00-8:00
8:00-9:00
9:00-10:00
10:00-11:00 1 10%
11:00-12:00 1 10%
12:00-13:00
13:00-14:00
14:00-15:00
15:00-16:00
16:00-17:00
17:00-18:00 2 20%
18:00-19:00 1 10%
19:00-20:00
20:00-21:00
21:00-22:00 1 10%
22:00-23:00
23:00-24:00
Table 42 identifies a significant trend at this intersection. A majority of the crashes
occurred at night, and the intersection is not lighted at night.
Table 42: Day and night crash summary for Delaware 15 & Andrews Lake Road
Time of Day Number of Crashes Percentage
Day 4 40%
Night 6 60%
41
Table 43 shows that Thursday and Saturday are the days on which the greatest number of
crashes have occurred at Delaware 15 & Andrews Lake Road. However, this trend does not seem
significant because crashes also occurred frequently on other days of the week.
Table 43. Day of week of crashes at Delaware 15 & Andrews Lake Road
Day of Week Number of Crashes Percentage
Sunday 1 10%
Monday 1 10%
Tuesday 2 20%
Wednesday
Thursday 3 30%
Friday
Saturday 3 30%
Table 44 demonstrates that 40% of the crashes at Delaware 15 & Andrews Lake Road
happened during October. While this is a large percentage of the crashes, the data does not
suggest a seasonal pattern in crashes that needs to be addressed at this intersection due to the fact
that other fall months do not have the same high crash rate and inclement road conditions that
could be a problem during the later fall months do not correlate to the increased crash rate in this
circumstance.
42
Table 44. Month of year of crashes at Delaware 15 & Andrews Lake Road
Month of the Year Number of Crashes Percentage
January 1 10%
February
March 2 20%
April
May 1 10%
June
July
August 1 10%
September
October 4 40%
November
December 1 10%
Table 45 shows the distribution of the age of drivers who were determined to be
responsible for the crashes at Delaware 15 & Andrews Lake Road. As is consistent with standard
safety statistics, younger drivers were responsible for the greatest number of crashes at this
intersection.
Table 45. Age of drivers responsible for crash at Delaware 15 & Andrews Lake Road
Age Number of Crashes Percentage
16-19 3 30%
20-29 3 30%
30-39 1 10%
40-49
50-59
60-69
70 and older 2 20%
Unknown 1 10%
Table 46 below shows that the distribution of the ages of all drivers involved in crash is
relatively evenly distributed with younger drivers being more represented due to their tendency
to cause crashes as shown previously in Table 45.
43
Table 46. Age of all drivers involved in crashes at Delaware 15 & Andrews Lake Road
Age Number of Crashes Percentage
16-19 4 20%
20-29 6 30%
30-39 1 5%
40-49 2 10%
50-59 3 15%
60-69 1 5%
70 and older 2 10%
Unknown 1 5%
Table 47 shows that the weather was clear when most of the crashes occurred at
Delaware 15 & Andrews Lake Road. During two of the crashes visibility was compromised by
fog or rain.
Table 47. Weather during crashes at Delaware 15 & Andrews Lake Road
Weather Number of Crashes Percentage
Rain 1 10%
Cloudy 2 20%
Clear 6 60%
Fog 1 10%
As shown in Table 48, the roads were dry during the vast majority of the crashes at
Delaware 15 & Andrews Lake Road.
Table 48. Road conditions during crashes at Delaware 15 & Andrews Lake Road
Road Condition Number of Crashes Percentage
Wet 1 10%
Dry 9 90%
Table 49 shows the occurrence of alcohol related crashes at Delaware 15 & Andrews
Lake Road. It does not appear that impaired driving is a significant trend at this intersection.
44
Table 49. Alcohol related crashes at Delaware 15 & Andrews Lake Road
Number of Crashes Percentage
Alcohol Related 1 10%
Not Alcohol Related 9 90%
It became apparent that the likely reasons for the high crash rate at the intersection are a
combination of the angle of intersection between Delaware 15 and Andrews Lake Road and a
lack of visibility at night.
6.3. Suggested Countermeasures and Projected Effectiveness
One possible countermeasure could be to reconfigure the intersection so that the two
roads intersect at a 90 degree angle. When an roads at an unsignalized intersection do not meet at
90 degree angles, drivers are forced to turn their vehicle a greater angle than they would typically
expect from some of the approaches. This motion is contrary to driver expectations and can
result in drivers not allowing enough time to complete the movement in front of oncoming traffic
or making the maneuver too quickly. The Highway Safety Manual recognizes the increased
potential for danger at skewed intersections and suggests realigning the intersection in cases
where the skew angle is very large or the intersection is frequently the location of crashes. The
intersection currently has a skew angle of 40 degrees meaning that the roads intersect at a 50
degree angle, or 40 degrees away from 90 degrees. Given the 40 degree skew angle, the crash
modification factor can be found using Equation 2.
Equation 2
The crash modification factor is determined to be 0.806 for all types and severity of crashes if the
40 degree skew angle were reduced to zero. See Table 50 below for the expected crash reduction
for reduction of skew angle.
45
Table 50. Expected crashes with reduction of skew angle
Expected crashes per year
with no treatment
Expected crashes per year
with reduction of skew angle
All Crashes 3.33 2.68
Another countermeasure that would be effective at this intersection is installing lighting
since a large percentage of crashes occur during the night. The calculation for the crash
modification factor for adding lighting to an intersection is shown in Equation 3.
Equation 3
The proportion of night crashes, Pni, for this intersection is 0.6 and the calculated crash
modification factor is 0.772 for all crashes. The Highway Safety Manual gives a CMF value of
0.62 and standard error of 0.04 for injury crashes when lighting is added to an intersection. See
Table 51 below for the expected crash reduction with the addition of lighting to the intersection.
The values in parenthesis represent a 95 percent confidence interval.
Table 51. Expected crash reduction for addition of intersection lighting
Expected crashes per year
with no treatment
Expected crashes per year
with intersection lighting
All Crashes 3.33 2.57
Injury Crashes 1.67 1.04 (0.70-1.37)
A third option to reduce the crash rate at this intersection would be to both reduce the
skew angle of the intersection and add intersection lighting. While it has been proven that
employing multiple countermeasures at an intersection typically reduces the crash rate beyond
what any one of the countermeasures does on its own, the magnitude of the reduction is
46
uncertain. Therefore, the crash reduction potential of combining reducing the intersection skew
angle with adding intersection lighting cannot be accurately quantified.
A final suggestion to reduce the crash rate at this intersection is through checking the
retroreflectivity, or visibility at night, of the signs and pavement marking in the area of the
intersection. This option is much less expensive and less disruptive to traffic at the intersection
than the previous countermeasures. If the signs or pavement markings are not visible at night,
they can be replaced or refurbished in an effort to reduce the number of night crashes at
Delaware 15 & Andrews Lake Road. Checking the night visibility also could be completed prior
to pursuing the more costly improvements suggested earlier in this section.
6.4 Cost/ Benefit Analysis
Crashes at Delaware 15 & Andrews Lake Road could be reduced through decreasing the
skew angle of the intersection or by illuminating the intersection at night using intersection
lighting. Table 52 below summarizes the calculations for the expected yearly monetary benefit of
crash reduction at Delaware 15 & Andrews Lake Road through the realignment of the
intersection to decrease the skew angle to zero.
47
Table 52. Monetary value of crash reduction for removal of skew angle at Delaware 15 &
Andrews Lake Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
1.67 0.32 $50,624
Property Damage
Only Crashes
1.67 0.32 $2,368
TOTAL $52,992
Using Equation 1, the expected monetary benefit over ten years resulting from crash
reduction at Delaware 15 & Andrews Lake Road due to removing the skew angle is $429,813.
Table 53 summarizes the calculations of the monetary value of crash reduction for the
countermeasure of adding lighting to the intersection at Delaware 15 & Andrews Lake Road.
Table 53. Monetary value of crash reduction for installation of intersection lighting at Delaware
15 & Andrews Lake Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
1.67 0.63 $99,666
Property Damage
Only Crashes
1.67 0.38 $2,812
TOTAL $102,478
Using Equation 1 to calculate the present value of the monetary benefits of adding
lighting at the intersection of Delaware 15 & Andrews Lake Road over ten years, the benefit to
society through crash reduction was found to be $831,188.
48
The cost of installing lighting at an intersection ranges between $100,000 and $150,000.
The variation is due to the specific characteristics of the site and whether electrical wires are
already near the area. There is also a cost to power the lights that continues over the lifetime of
the lights. Depending on electricity prices, the cost per month for electricity for an intersection is
$20-$40. Over the course of a year this amounts to $240-$480. When converting that cost
distributed over ten years to a present value using Equation 1, the additional maintenance cost of
operating the lights range from $1,950 to $4,000.
The cost of realigning an intersection is very site specific. In order to estimate the cost of
realigning Delaware 15 & Andrews Lake Road, a planning level cost estimate was calculated
using RS Means 2012 unit costs and estimated construction amount values. See Table 54 for a
summary of the cost estimate calculations.
Table 54. Cost estimate for intersection realignment at Delaware 15 & Andrews Lake Road
Item Unit Cost Estimated Quantity Cost
Clearing and grubbing $6,500/ acre 12 $78,000
Excavation $33/ CY 1000 $33,000
Subbase $12/ SY 1000 $12,000
Asphalt paving $23/ SY 1000 $23,000
Line striping $0.50/ LF 6000 $3,000
Removal of existing roadway $33/ CY 1000 $33,000
Top soil/ grass seed $12/ SY 10,000 $120,000
Mobilization $302,000*0.15 $45,300
Traffic Management Flaggers, cones, barrels, signs, etc $30,000
A total cost of $350,000 for realigning the intersection was estimated. Relocating utilities and
drainage costs would escalate the price of intersection realignment to $500,000 to $1,000,000.
This range was used in Table 55 below to calculate the cost to benefit ratio for realigning the
intersection to remove the skew angle.
49
Table 55. Cost to benefit ratio for proposed Delaware 15 & Andrews Lake Road
countermeasures
Countermeasure Cost Benefits Cost: Benefit
Ratio (lower
bound)
Cost: Benefit
Ratio (upper
bound)
Add intersection
lighting
$100,000-
$150,000
$831,188 1:5.5 1:8.3
Reduce skew
angle
$500,000-
$1,000,000
$429,813 1:0.4 1:0.9
As shown in Table 55, adding intersection lighting is expected to have a greater cost to
benefit ratio than reducing the skew angle of the intersection through a realignment of the
intersection.
50
7. Delaware 30 & Mount Joy Road
Figure 10. Delaware 30 and Mount Joy Road location map
7.1 Site Overview and Site Visit Observations
Delaware 30 & Mount Joy Road is located outside of Millsboro, Delaware in Sussex
County. Delaware 30 travels in the northbound and southbound directions and is known as
Gravel Hill Road in the vicinity of the intersection. Mount Joy Road is the name of the crossroad
from the westbound approach, and Morris Mill Road is the name of the street from the eastbound
approach. The AADT value for Delaware 30 is 3,900 vehicles per day, and the AADT for Mount
Joy Road is 2,600. As of January 2012, the traffic on Mount Joy Road had a stop sign at the
intersection, but the traffic on Delaware 30 did not stop. Nine crashes occurred at this
intersection over the past three years with five crashes occurring in 2010. One fatality was
recorded at this intersection.
51
The site visit showed that sight distance from the eastbound and westbound approaches is
slightly obscured by telephone poles. The northbound and southbound approaches to the
intersection have an intersection warning sign with flashing yellow lights. The eastbound and
westbound approaches have flashing red lights on the stop sign at the intersection with Delaware
30. There is one lane in each direction from each approach. The speed limit is 50 mph from all
four approaches. There is passing permitted nearby in the northbound and southbound directions.
There is a curve approaching the intersection from the westbound approach, but there are
minimal vertical grades at the intersection. There is no lighting at the intersection.
7.2 Intersection Trends and Reasons for Crash Analysis
The most common type of crash at Delaware 30 & Mount Joy Road is vehicles that fail to
remain stopped on Mount Joy Road until Delaware 30 is clear to cross. As shown in Table 56
below, vehicles that fail to remain stopped account for two thirds of the crashes at the
intersection.
Table 56. Type of crash summary at Delaware 30 & Mount Joy Road
Type of Crash Frequency Percentage
Failure to remain stopped 6 66.7%
Ran stop sign 2 22.2%
Inattentive driving 1 11.1%
While a significant proportion of the reasons for crashes at Delaware 30 & Mount Joy
Road were determined to be unknown, the largest reason for crash at the intersection was drivers
who did not see conflicting traffic before making an unsafe turning maneuver. Most frequently,
the drivers did not see traffic approaching in the southbound direction. Table 57 summarizes the
reasons for crash at Delaware 30 & Mount Joy Road.
52
Table 57. Reason for crash summary at Delaware 30 & Mount Joy Road
Reason for Crash Frequency Percentage
Didn’t see vehicle NB: 1 NB: 11.1%
SB: 3 SB: 33.3%
Wet road 1 11.1%
Unknown 4 44.4%
As shown by Table 58, the crashes at Delaware 30 & Mount Joy Road were primarily
caused by drivers from the eastbound and westbound minor road approaches. Of the crashes that
occurred as a result of drivers entering the intersection from the minor road approaches, more
crashes were due to drivers coming from the eastbound approach, but crashes were nearly evenly
distributed between both the eastbound and westbound approaches.
Table 58. Approach of driver responsible for crashes at Delaware 30 & Mount Joy Road
Direction Frequency Percentage
Northbound 0 0%
Southbound 1 11.1%
Eastbound 5 55.6%
Westbound 3 33.3%
Table 59 shows that Delaware 30 & Mount Joy Road has had a history of severe crashes.
Nearly 80% of the crashes that occurred at this intersection resulted in personal injury or fatality.
The fatal crash was due to a driver who failed to stop at the stop sign from the eastbound
approach and struck a vehicle on Delaware 30. This is the only intersection in the study that has
reported a fatality.
Table 59. Crash severity at Delaware 30 & Mount Joy Road
Severity Frequency Percentage
Property Damage Only 2 22.2%
Personal Injury 6 66.7%
Fatality 1 11.1%
53
Table 60 shows that crashes at Delaware 30 & Mount Joy Road most frequently occur
during the traditional afternoon peak hours. This trend does not represent anything out of the
ordinary as traffic volumes also are typically greatest during this time period.
Table 60. Time of day of crash at Delaware 30 & Mount Joy Road
Time Number Of Crashes Percentage
0:00-1:00
1:00-2:00
2:00-3:00
3:00-4:00
4:00-5:00
5:00-6:00
6:00-7:00 1 11.11%
7:00-8:00
8:00-9:00
9:00-10:00
10:00-11:00
11:00-12:00 1 11.11%
12:00-13:00 2 22.22%
13:00-14:00
14:00-15:00
15:00-16:00
16:00-17:00 2 22.22%
17:00-18:00 1 11.11%
18:00-19:00 1 11.11%
19:00-20:00
20:00-21:00
21:00-22:00
22:00-23:00
23:00-24:00 1 11.11%
As shown in Table 61, the majority of the crashes at Delaware 30 & Mount Joy Road
occur during the day which suggests that nighttime visibility at this intersection is not a problem.
54
Table 61. Period of day of crashes at Delaware 30 & Mount Joy Road
Time of Day Number of Crashes Percentage
Day 7 77.78%
Night 1 11.11%
Dawn 1 11.11%
Table 62 below shows the distribution of crashes at Delaware 30 & Mount Joy Road over
the days of the week. The number of crashes on each day are nearly evenly distributed.
Table 62. Day of week of crashes on Delaware 30 & Mount Joy Road
Day of Week Number of Crashes Percentage
Sunday 1 11.11%
Monday 1 11.11%
Tuesday 2 22.22%
Wednesday 2 22.22%
Thursday 1 11.11%
Friday
Saturday 1 11.11%
Table 63 demonstrates that crashes at Delaware 30 & Mount Joy Road tend to happen
during the summer and fall months.
Table 63. Month of crashes at Delaware 30 & Mount Joy Road
Month of the Year Number of Crashes Percentage
January
February
March
April
May
June 2 22.22%
July 4 44.44%
August
September 1 11.11%
October 2 22.22%
November
December
55
During the past twenty years, southern Delaware has seen an increase in retirees moving
to the area. Since elderly drivers are typically at a higher risk for crashes, the age of drivers
involved in crashes was suspected to be a primary concern at Delaware 30 & Mount Joy Road.
However, as Table 64 shows, elderly drivers were not the main cause of crashes. Drivers in the
20-29 age group caused more crashes at this intersection than drivers 60 and older.
Table 64. Age of drivers responsible for crashes at Delaware 30 & Mount Joy Road
Age Number of Crashes Percentage
16-19 1 11.11%
20-29 3 33.33%
30-39 1 11.11%
40-49 1 11.11%
50-59 1 11.11%
60-69 0 0%
70 and older 2 22.22%
Table 65 shows the distribution of the age of all drivers involved in crashes at Delaware
30 & Mount Joy Road. While middle aged drivers are underrepresented for causing crashes, it
seems as though drivers of all ages are involved in crashes at this intersection. Elderly drivers do
not appear to be involved in crashes at this location more frequently than drivers of other ages.
Table 65. Age of all drivers involved in crashes at Delaware 30 & Mount Joy Road
Age Number of Crashes Percentage
16-19 1 5.56%
20-29 6 33.33%
30-39 1 5.56%
40-49 2 11.11%
50-59 6 33.33%
60-69
70 and older 2 11.11%
56
Table 66 shows the weather conditions at Delaware 30 & Mount Joy Road during
crashes. Most of the crashes at this intersection occurred when the sky was clear.
Table 66. Weather conditions during crashes at Delaware 30 & Mount Joy Road
Weather Number of Crashes Percentage
Cloudy 1 11.11%
Rainy 1 11.11%
Clear 7 77.78%
Table 67 shows that the roads were dry during nearly all of the crashes at Delaware 30 &
Mount Joy Road.
Table 67. Road conditions during crashes at Delaware 30 & Mount Joy Road
Road Condition Number of Crashes Percentage
Wet 2 22.22%
Dry 7 77.78%
As shown in Table 68, no crashes at Delaware 30 & Mount Joy Road were attributed to
impaired drivers.
Table 68. Alcohol related crashes at Delaware 30 & Mount Joy Road
Number of Crashes Percentage
Alcohol Related 0 0%
Not Alcohol Related 9 100%
After reviewing, the crash reports and site visits it appears that crashes at Delaware 30 &
Mount Joy Road were mainly due to drivers on Mount Joy Road who attempted to cross
Delaware 30 when there was not a large enough gap in traffic.
57
7.3 Suggested Countermeasures and Projected Effectiveness
As of February 2012, DelDOT converted the intersection from a two way stop to all way
STOP. Employing this countermeasure makes sense for this intersection because many crashes at
this intersection are the result of drivers on the minor road not waiting until a large enough gap is
present to cross the intersection. A four way stop would eliminate the need for drivers on Mount
Joy Road to determine when the gap between the traffic on Delaware 30 is large enough to enter
the intersection. Drivers at the minor road approaches at this intersection also claimed to have
difficultly seeing drivers on Delaware 30. If the traffic on Delaware 30 were forced to stop at the
intersection with Mount Joy Road, these types of crashes could be reduced. Using the predictive
method in the Highway Safety Manual, the crash modification factor for converting a rural,
minor road stop controlled intersection to all-way stop control is 0.52 for all crashes with a
standard error of 0.04. Table 69 below shows the expected number of crashes per year at
Delaware 30 & Mount Joy Road after the all way stop conversion.
Table 69. Conversion to all way stop control at Delaware 30 & Mount Joy Road
Expected crashes per year
with no treatment
Expected crashes per year
with all-way STOP conversion
All Crashes 3 1.56 (1.44-1.68)
When observing the crash trends at Delaware 30 & Mount Joy Road, it is important to
note that crashes at this location may increase slightly immediately following the conversion to
all way stop control. Rear end crashes on Delaware 30 are likely to increase due to drivers who
have driven through this intersection many times and do not expect a vehicle in front of them
stopped at a stop sign. Likewise, it is also possible that a few inattentive drivers will run the stop
sign on Delaware 30 prior to adjusting to the new stop signs. These transition consequences
58
could be mitigated through adding STOP AHEAD signs or drawing attention to the new stop
signs using flashing lights. After a short period of time, crashes are expected to decrease to the
values shown in Table 69.
7.4 Cost/ Benefit Analysis
The conversion of Delaware 30 & Mount Joy Road to an all way stop controlled
intersection has been shown through previous calculations to reduce the crash rate. Table 70
below shows the estimated monetary value of the expected crash reduction at this location using
the Highway Safety Manual’s methodology.
Table 70. Monetary value of crash reduction due to conversion to an all way stop at Delaware 30
& Mount Joy Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
2.33 1.12 $177,184
Property Damage
Only Crashes
0.67 0.32 $2,368
TOTAL $179,552
Using Equation 1, the present value of the expected monetary value of crash reduction
due to converting Delaware 30 & Mount Joy Road into an all way stop is $1,456,328.
The estimated cost of converting Delaware 30 & Mount Joy Road to a four way stop and
improving the pavement markings is $100-$1,000. Following the initial intersection remediation
it is expected that little to no added maintenance cost would result. See Table 71 for a summary
of the calculations for the cost to benefit ratio of converting the intersection to a four way stop.
59
Table 71. Cost to benefit ratio of converting Delaware 30 & Mount Joy Road to a four way stop
Countermeasure Cost Benefits Cost: Benefit
Ratio (lower
bound)
Cost: Benefit
Ratio (upper
bound)
Conversion to
four way stop
$100-$1,000 $1,456,328 1:1,456.3 1:14,563.3
As shown in Table 71, converting Delaware 30 & Mount Joy Road is expected to have
substantial financial benefits over the next ten years.
60
8. Delaware 30 & Zoar Road
Figure 11. Delaware 30 and Zoar Road location map
8.1 Site Overview and Site Visit Observations
The intersection of Delaware 30 & Zoar Road is located approximately one mile north of
Delaware 30 & Mount Joy Road also outside of Millsboro, Delaware in Sussex County.
Delaware 30 is the northbound and southbound approaches to the intersection and is still referred
to as Gravel Hill Road at the intersection of Zoar Road. Zoar Road is the name of the eastbound
and westbound approaches to the intersection. The AADT on Delaware 30 is 3,900, and the
AADT on Zoar Road is 2,800. As of January 2012, the traffic on Zoar Road stopped at a stop
sign at the intersection with Delaware 30, and the traffic at Delaware 30 did not stop. Seventeen
61
crashes have occurred at the intersection of Delaware 30 and Zoar Road during the past three
years.
The site visit revealed that many intersection awareness measures have been installed at
this location with limited success. There are overhead flashing beacons at the intersection which
flash yellow lights in the northbound and southbound directions and red lights in the eastbound
and westbound directions. There are rumble strips on the eastbound and westbound approaches,
but the rumble strips seem to close to the intersection (especially from the westbound approach)
and not very effective at alerting the vehicles as they pass over them. The speed limit is 50 mph
for all approaches to the intersection. Passing is permitted in the vicinity of the intersection from
all approaches. Signs block some of the sight distract from the westbound approach. The
intersection is not lighted but the flashing beacons illuminate the intersection.
8.2 Intersection Trends and Reasons for Crash Analysis
Table 72 summarizes the types of crashes that occurred at Delaware 30 & Zoar Road.
Drivers who failed to remain stopped at the stop sign on Zoar Road before crossing the
intersection comprised the largest percentage of type of crash at the intersection. A sign is
located near the intersection to warn drivers of the presence of deer in the area since two of the
crashes near this intersection involved collision with a deer.
Table 72. Types of crash summary at Delaware 30 & Zoar Road
Type of Crash Frequency Percentage
Failure to remain stopped 10 58.8%
Failure to yield right of way 2 11.8%
Deer in roadway 2 11.8%
Ran off road 1 5.9%
Careless driving 1 5.9%
Inattentive driving 1 5.9%
62
As shown in Table 73, the most frequent reason for crash at Delaware 30 & Zoar Road
was drivers who did not see cross traffic, particularly from the northbound direction. It is also
important to note that multiple drivers who had a crash at this intersection expected the
intersection to be a four way stop.
Table 73. Reason for crash summary at Delaware 30 & Zoar Road
Reason for Crash Frequency Percentage
Didn’t see vehicle NB: 4 NB: 23.6%
SB: 2 SB: 11.8%
Expected four way stop 2 11.8%
Sun blocked view 1 5.9%
Large vehicle blocked view 1 5.9%
Vehicle travelling in wrong
lane
1 5.9%
Driving too fast to turn 1 5.9%
Debris on roadway 1 5.9%
Driver wasn’t paying attention 1 5.9%
None 2 11.8%
Unknown 1 5.9%
Table 74 shows the approach direction of vehicles responsible for crashes at Delaware 30
& Zoar Road. More crashes occur due to vehicles from the minor road approaches from the
eastbound and westbound directions than on the major road approaches. Crashes are evenly
distributed between both minor road and both major road approaches.
Table 74. Approach of drivers responsible for crashes on Delaware 30 & Zoar Road
Direction Frequency Percentage
NB 2 11.8%
SB 3 17.6%
EB 6 35.3%
WB 6 35.3%
63
Table 75 shows that more than half of the crashes at Delaware 30 & Zoar Road cause
only damage to property and no injury to passengers in the vehicle(s).
Table 75. Crash severity at Delaware 30 & Zoar Road
Severity Frequency Percentage
Property Damage Only 10 58.8%
Personal Injury 7 41.2%
As shown by Table 76, crashes are mainly clustered around the typical morning and
afternoon peak travel hours which is a common trend since traffic volumes are usually greatest
during those hours.
Table 76. Time of day of crashes at Delaware 30 & Zoar Road
Time Number Of Crashes Percentage
0:00-1:00
1:00-2:00
2:00-3:00
3:00-4:00
4:00-5:00
5:00-6:00
6:00-7:00 1 5.88%
7:00-8:00 2 11.76%
8:00-9:00 2 11.76%
9:00-10:00
10:00-11:00 2 11.76%
11:00-12:00
12:00-13:00
13:00-14:00 1 5.88%
14:00-15:00 2 11.76%
15:00-16:00
16:00-17:00 4 23.53%
17:00-18:00 1 5.88%
18:00-19:00
19:00-20:00 1 5.88%
20:00-21:00
21:00-22:00 1 5.88%
22:00-23:00
23:00-24:00
64
Table 77 shows the division between crashes that occur during the day and crashes that
occur at night. The majority of crashes at Delaware 30 & Zoar Road occurred during the day
when the intersection was lit by natural sunlight.
Table 77. Period of day of crashes at Delaware 30 & Zoar Road
Time of Day Number of Crashes Percentage
Day 14 82.35%
Night 3 17.65%
Table 78 shows that the most common day for crashes at Delaware 30 & Zoar Road is
Thursday and no crashes occurred on Saturdays. However, this trend does not seem to be
correlated to any other intersection trends or design features.
Table 78. Day of week of crashes at Delaware 30 & Zoar Road
Day of Week Number of Crashes Percentage
Sunday 1 5.88%
Monday 2 11.76%
Tuesday 2 11.76%
Wednesday 3 17.65%
Thursday 6 35.29%
Friday 3 17.65%
Saturday
Table 79 shows that the highest concentration of crashes occurs in the first months of the
year with the greatest number of crashes occurring in March.
65
Table 79. Month of year of crashes at Delaware 30 & Zoar Road
Month of the Year Number of Crashes Percentage
January 3 17.65%
February 2 11.76%
March 4 23.53%
April 2 11.76%
May
June 1 5.88%
July 1 5.88%
August 1 5.88%
September
October 1 5.88%
November 1 5.88%
December 1 5.88%
As a result of the trend of elderly drivers moving to Sussex Count, it was considered
probable that Delaware 30 & Zoar Road could have an increased occurrence of crashes due to
elderly drivers. After analyzing the age of the drivers involved in crashes, it was determined that
there is a large number of crashes occurring at this intersection involving elderly drivers. As
illustrated by Table 80, over 40% of the crashes at Delaware 30 & Zoar Road were caused by
drivers over age 60.
Table 80. Age of drivers responsible for crashes at Delaware 30 & Zoar Road
Age Number of Crashes Percentage
16-19
20-29 2 14.29%
30-39 2 14.29%
40-49 1 7.14%
50-59 1 7.14%
60-69 4 28.57%
70 and older 2 14.29%
66
Table 81 below shows the age of all drivers involved in crashes at Delaware 30 & Zoar
Road. More middle aged drivers are involved in crashes and not determined to be responsible for
the crashes than are the cause of the crashes as shown by comparing Table 81 with Table 80.
Table 81. Age of all drivers involved in crashes at Delaware 30 & Zoar Road
Age Number of Crashes Percentage
16-19 3 10.71%
20-29 3 10.71%
30-39 4 14.29%
40-49 6 21.43%
50-59 3 10.71%
60-69 5 17.86%
70 and older 2 7.14%
As shown in Table 82, nearly all of the crashes at Delaware 30 & Zoar Road occurred
with the weather was clear.
Table 82. Weather during crashes at Delaware 30 & Zoar Road
Weather Number of Crashes Percentage
Clear 16 94.12%
Rainy 1 5.88%
Table 83 shows that poor road conditions do not greatly increase the crash rate at
Delaware 30 & Zoar Road.
Table 83. Road conditions during crashes at Delaware 30 & Zoar Road
Road Condition Number of Crashes Percentage
Wet 2 11.76%
Dry 15 88.24%
67
As shown by Table 84, none of the crashes at Delaware 30 & Zoar road during the past
three years were the result of impaired drivers.
Table 84. Alcohol related crashes at Delaware 30 & Zoar Road
Number of Crashes Percentage
Alcohol Related 0 0%
Not Alcohol Related 17 100%
Other factors which could potentially impact the crash frequency at Delaware 30 & Zoar
Road such as age of drivers, weather conditions, road conditions, approach of drivers, time of
day, day of week, and month of year were also considered. None of these factors proved
significant, but tables summarizing the analysis can be found in the Appendix.
8.3 Suggested Countermeasures and Projected Effectiveness
In February 2012, DelDOT installed stop signs to convert the intersection to an all way
stop. This countermeasure fits the crash trends at Delaware 30 & Zoar Road because many
crashes were caused by drivers entering the intersection when there was not a large enough gap
in the cross traffic. Also, other low cost improvements to the intersection including flashing
overhead beacons and rumble strips were not effective at reducing crashes. Some drivers stated
that they expected the traffic on Delaware 30 to stop prior to the February 2012 conversion to an
all way stop intersection. Now that the intersection is an all way stop, it may be more in line with
driver expectation. Using the predictive method in the Highway Safety Manual, the crash
modification factor for converting a rural, minor road stop controlled intersection to all-way stop
control is 0.52 for all crashes with a standard error of 0.04. Table 85 below shows the expected
number of crashes per year at Delaware 30 & Mount Joy Road after the all way stop conversion.
68
Table 85. Conversion to all way stop control at Delaware 30 & Zoar Road
Expected crashes per year
with no treatment
Expected crashes per year
with all-way STOP conversion
All Crashes 5.67 2.95 (2.72 - 3.17)
It is also important to note that the number of crashes experienced at this intersection
could increase slightly right after the initial installation of the two new stop signs due to drivers
who are familiar with the area, but not aware that the intersection has become an all way stop.
However, after a short period of transition time, crashes at Delaware 30 & Zoar Road should
reduce as per the calculations in Table 85.
Delaware 30 & Zoar Road currently has flashing beacons above the intersection and
rumble strips from the minor approaches that were implemented with the intention of reducing
crashes. However, the site visit revealed that the rumble strips appeared to be too close to the
stop sign and worn down. It is suggested that the spacing and location of the rumble strips be
investigated to determine if they meet current standards. Retrofitting or replacing the rumble
strips to restore quality and ensuring they meet the state standards could improve the safety of
this intersection.
Numerous studies have been performed regarding the impact of flashing beacons on
crash reduction. It has been shown that overhead flashing beacons are more effective than
flashing beacons above signs. However, the studies have shown that crash reduction from all
types of flashing beacons is typically limited and highly variable due to multiple reasons. While
flashing beacons attract attention to the intersection initially, over time, their effectiveness
decreases as drivers get used to their presence. Also, the flashing yellow light often displayed
overhead from on the major road approach like the ones at Delaware 30 & Zoar Road can
encourage drivers to speed up in an effort to “beat the yellow light” as they might at a signalized
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intersection. The Highway Safety Manual acknowledges the variability of flashing beacons when
offering values for crash modification factors. Table 86 shows the values the Highway Safety
Manual gives for crash modification factors for overhead flashing beacons. The term “All
Settings” refers to locations in either rural or urban locations.
Table 86. Highway Safety Manual crash modification factors for overhead flashing beacons
Crash Modification Factor Standard Error
All Settings, All Severities 0.95* 0.04
All Settings, Injury 0.90* 0.06
All Settings, Rear End 0.92* 0.1
All Settings, Angle 0.87 0.06
Rural, Angle 0.84 0.06
Crash modification factors marked with asterisks are identified as cases in which the
addition of flashing beacons could result in an increase, decrease, or no change in the crash
frequency at the intersection. In the case of rural locations, the crash rate is expected to decrease,
but given the crash modification factor and large standard error, it is possible that the crash
reduction experienced at an intersection such as Delaware 30 & Zoar Road be nearly negligible.
8.4 Cost-Benefit Analysis
As shown in the table above, converting Delaware 30 & Zoar Road into an all way stop
controlled intersection, is expected to reduce the crash rate at the intersection. Using the
Highway Safety Manual methodology, the yearly monetary benefit of the expected crash
reduction was calculated and shown in Table 87.
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Table 87. Monetary value of crash reduction due to conversion to an all way stop at Delaware 30
& Zoar Road
Type of Crash Current Crash Rate
(per year)
Crashes Prevented
Through
Countermeasure
(per year)
Monetary Benefit of
Crash Reduction
(per year)
Fatality/ Injury
Crashes
2.33 1.12 $177,184
Property Damage
Only Crashes
3.33 1.60 $11,840
TOTAL $189,024
Using Equation 1, the present value of the expected monetary value to society of the
crash reduction at Delaware 30 & Zoar Road through the conversion of the intersection to an all
way stop is $1,533,154 over ten years.
The cost of converting Delaware 30 & Zoar Road into a four way stop controlled
intersection through adding signs and improving the pavement markings is estimated to cost
$100-$1,000. This improvement would have little to no maintenance costs following the initial
improvement, so it is assumed that the initial cost will be the whole cost of the project over ten
years. See Table 88 for a summary of the cost to benefit ratio calculations for this intersection.
Table 88. Cost to benefit ratio for converting Delaware 30 & Zoar Road to a four way stop
Countermeasure Cost Benefits Cost: Benefit
Ratio (lower
bound)
Cost: Benefit
Ratio (upper
bound)
Convert to four
way stop
$100-$1,000 $1,533,154 1:1,533.2 1:15,331.5
The payoff expected from reducing the crash rate at this intersection is estimated to be
between 191.6 and 306.6 times greater than the cost of the improvements to the intersection.
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9. Overall Observations and Conclusions
An overarching trend exhibited by all five of the intersections studied is that the main
cause of crash was drivers who stopped at the stop sign as expected, but continued into the
intersection when cross traffic was blocking the intended travel path of the vehicle. This driver
error was due largely to the inattention of the drivers. In many cases, drivers on one of the minor
road approaches failed to adequately observe vehicles on the major road. At all of the
intersections studied besides Delaware 15 & Barratts Chapel Road, the major road has a speed
limit of 50 mph. Therefore, the traffic on the major road is moving quickly and can cause serious
crashes if a vehicle on the major road strikes a vehicle on the minor road. Also, drivers travelling
quickly on the major road would likely not be able to avoid a driver entering or crossing the road
from the minor approach. In the case of some of the intersections, passing is allowed on the
major road which may encourage drivers to travel at speeds above the posted speed limit in the
vicinity of the intersections.
Another factor that could be influencing the recent increase in crashes at the intersections
in this study could be due to an increase in traffic volume in the area. While all of the
intersections are located in rural areas, new housing subdivisions continue to carve up rural land
thereby increasing the volume of traffic on rural roads. Drivers who have lived near the
intersections in this study for many years may not be aware of the increased traffic volume in
recent years. As a result, the heightened danger that the increased traffic volume poses is
discounted by drivers who have traversed the intersection safely countless times before.
Similarly, drivers who are not familiar with the area could also underestimate the volume of
traffic when crossing heavily travelled roads by not being as observant and alert as they should
be.
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Delaware Center for Transportation University of Delaware Newark,
Delaware 19716
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