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\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
CSAH 30 and Braddock Trail – Intersection Assessment
Review by: Kevin Collins, Senior Traffic Technician, Dakota County and Kristi Sebastian, PE, PTOE ,
Dakota County Traffic Engineer
Evaluation Conducted Fall 2015 – March 2016
Improvement recommendations for the County CIP summary – July 2016
Reason for Study: The original concern at this intersection in the summer of 2015 was related to signing
and marking inconsistency on the northbound approach. Old pavement markings that were previously
covered over became visible again, creating an unintended lane assignment for the northbound
approach. This issue was resolved in August of 2015 with the removal of the through arrow in the right
most lanes and moving it to the left most lane to go northbound. The change addressed the left turn
type collisions occurring at the intersection.
In addition to addressing this issue, other concerns were raised regarding pedestrians and side road
traffic operation including the request for adding left turn arrows. Traffic staff assessed the intersection
regarding concerns for overall operation, pedestrian safety and operation for the traffic along Braddock
Trail turning onto or crossing CSAH 30.
Existing Traffic Control and Geometrics: The intersection of CSAH 30 and Braddock Trail is a signalized
intersection. The signal was installed in 1993. Eagan High School and Dakota Middle School are located
on the northwest side of the intersection with access to the schools from Braddock Trail. This creates
heavy turn movements and side road crossing movements in the morning when school is in session.
CSAH 30 is a four lane divided roadway with separate left turn lanes. The roadway narrows to one lane
in each direction with center left turn lanes east of Braddock Trail.
Braddock Trail was modified and signal revisions were made in 2012. This was done to align with
changes along Braddock Trail and to address the high eastbound left and southbound left turning
movements in the morning. The side road approaches have shared left/through lanes and separate
right turn lanes (See Appendix A -Existing Geometry). The approaches need to have the same lane
configuration to meet driver expectation and ensure safe operation. Therefore, to provide an exclusive
turn lane for southbound right turns to meet the high traffic volumes, the other lane must be a shared
left and through lane in both directions to provide a consistent message to drivers. If the northbound
lane were an exclusive left turn lane while the southbound lane remained a shared left/through lane,
northbound drivers would not expect through traffic to be approaching from the nearest lane.
\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
Traffic Volumes: A turning movement count was completed in May 2014; see Figure 1 below for AM
(7:00-8:00 a.m.) and PM (5:00-6:00 p.m.) peak hour volumes. While traffic is higher along CSAH 30 in
the afternoon, the turning movements from CSAH 30 to the north on Braddock Trail as well as the side
road traffic on Braddock Trail is highest in the morning when school is in session. The following graph
summarizes the morning turning movement volumes at the intersection:
Traffic Volume Figure 1: AM and PM peak hours – May 13, 2014
Crash Data: To evaluate safety at the intersection, a three year evaluation was conducted. This is the
typical evaluation period to assess trends and identify any potential issues as well as to provide standard
comparisons with other similar locations. The 2015 collision data was not available from the state. In
addition to evaluating recorded crash data, County staff discussed the intersection and safety concerns
with City engineering and law enforcement staff.
The crash rate at this intersection is 0.61crashes per million entering vehicles. This rate is lower than the
state crash rate of 0.69 for similar intersections. The severity rate for this intersection is 0.89. The
severity rate is also lower than the state severity rate of 0.96 for similar intersections. The majority of
collisions at this location were rear end and right angle crashes (77%). The majority of the rear end
crashes happened in the morning hours; right angle crashes occurred in the evening.
2011 to 2014 Crash Data (see attached collision diagram):
Year Right Angle Rear End Left Turn Sideswipe Total
2011 1 1 2
2012 2 2 4
2013 2 1 1 4
2014 1 1 1 3
Total 4 6 2 1 13
\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
Traffic Operations: Eagan High School and Dakota Hills Middle School are located just north of this
intersection. There is relatively low traffic along Braddock Trail from the neighborhood to the south,
except for the 6:30 a.m. to 8:00 a.m. time frame when school is in session. On school days, traffic
activity is higher for pedestrians, bicycles and motor vehicle in all directions during the morning
compared to other times of the year or other hours of the day. Likewise, traffic is also higher along
CSAH 30 at this time of day as motorists are traveling to work or to the school.
The existing traffic signal has timing plans in place to best address the traffic conditions during this time
of day. Traffic on Braddock Trail operates with permissive phasing; this means that left turn traffic must
yield to through traffic before proceeding. A signal revision in 2012 added a southbound right turn
green arrow that is concurrent with the eastbound left turn movement in order to reduce delay for this
heavy southbound right turn movement. The eastbound left turn is also a heavy move and requires a
large portion of the green time. Even with the large amount of time allocated, on occasion during the
morning peak hour while school is in session, eastbound left turning traffic can extend past the turn
lane into the through lane for eastbound CSAH 30.
Pedestrians are accommodated through cross walks throughout the intersection with pedestrian push
buttons to activate the pedestrian signal indications. With the 2012 signal revisions described above,
count down timers were added to provide pedestrians with information regarding when the time to
cross would be ending. This provides clarity for the pedestrians and bicyclists, including students
crossing in this area.
Left turn signal phasing, including left turn arrows to allow left turns to turn on an exclusive phase and
flashing yellow arrows to allow left turns after yielding to opposing traffic during lighter traffic times,
requires designated left turn lanes. The current configuration along Braddock Trail would need to be
modified to accommodate separate left turn lanes (See Appendix B – Proposed Geometry).
Field Observations: The primary focus of the citizen’s concern at the intersection related to the
northbound approach. The traffic observations reviewed these northbound operations.
Traffic observations were conducted by reviewing the video. They are summarized as follows:
• 6:30 a.m. to 8:00 a.m., October 28, 2015
o Weather Conditions were rainy.
o Volume was high.
o At several different times the left turn lane would have a long queue; however, most
times it cleared.
o There were several cars that would use the right turn lane as a thru lane when two or
more cars would queue up to make a left turn. It was noticed that once one car made
the maneuver several more cars would follow.
o There were a high number of left turns observed.
• 6:30 a.m. to 8:00 a.m., October 29, 2015
o Weather Conditions were rainy.
o Volume was high.
o There were long queues but all cleared.
o No motorists used the right turn lane as a through lane.
\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
o Northbound left turns were minimal during this time frame; this allowed the majority of
cars to make the through movement (to cross CSAH 30) with minimal delay or difficulty.
• 4:30 p.m. to 5:30 p.m., October 29, 2015
o Weather Conditions were overcast.
o Volumes were low.
o All cars used proper lanes to turn from Braddock Trail .
• 6:30 a.m. to 8:00 a.m., October 20, 2015
o Weather Conditions were overcast.
o Volume was high.
o There were long queues but all cleared.
o No motorists used the right turn lane as a thru lane.
o Northbound left turns were minimal during this time frame; this allowed the majority of
cars to make the through movement (cross CSAH 30) with minimal delay or difficulty.
o One motorist attempted to use the right turn lane as a through lane. At the same time,
two left turning cars cleared allowing the traffic waiting to cross CSAH 30 to proceed.
This resulted in the motorists which crossed improperly in the right lane needing to yield
to the traffic on his left before he could continue in the thru lane past the intersection.
Overall Field Review Summary: The operation worked very well throughout the day with no delay
except for the morning rush hour conditions for school days. During the morning rush hour, when traffic
volumes were high, northbound and southbound traffic would form longer queues which would
typically clear in the same cycle. The northbound traffic would typically navigate properly in conjunction
with left turners in order to proceed through the intersection. There were some occurrences observed
where traffic would use the right turn lane to pass left turning traffic, but this was not typical.
Capacity Evaluation: A signal analysis was conducted to determine traffic flow operation with existing
side road configuration on Braddock Trail and a proposed configuration of separate left, through and
right turn lanes southbound and a separate left plus a shared through/right turn lane northbound. With
the proposed configuration, left turn arrows to allow protected or permissive turns were assessed.
The high volume of traffic on CSAH 30 and heavy eastbound left turn movement in the morning rush
hour do not provide flexibility in giving any additional traffic signal time for Braddock Trail. Providing
exclusive left turns along Braddock Trail requires lane changes including a new southbound right turn
lane to provide a left turn only lane southbound. The northbound traffic could then be configured with
a left turn lane and shared through/right lane. While this configuration provides a better lane balance
based on traffic volumes, the left turn and through traffic would still be using the green time provided
for Braddock Trail today (no additional time can be used due to the heavy CSAH 30 volumes). The
following chart summarizes the level of service and delay. Level of service ranges from A (no delay) to F
(severe delay).
\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
Capacity Operation Summary:
Condition West
Approach
(EB)
East
Approach
(WB)
South
Approach
(NB)
North
Approach
(SB)
Overall
Existing Configuration - AM C (26.9 sec) C (32.4 sec) C (30.6) B (14.0) C (24.5)
Proposed Geometry – AM C (29.2 sec) C (34.9 sec) D (42.6) B (13.7) C (26.8)
Existing Configuration - PM B (12.8) C (21.6) C (21.0) B (12.6) B (15.8)
Proposed Geometry – PM B (13.6) C (21.8) C (22.3) B (10.5) B (15.9)
Level of Service (average delay per vehicle in seconds)
The simulation showed that adding the southbound right turn lane and exclusive left turns would result
in similar level of service compared to the existing condition. The higher level of service for the
southbound traffic reflects that the heavy right turn movement is receiving a green arrow concurrent
with eastbound traffic. While the south approach shows a slight increase in delay, in actual operation,
the efficiency of separating the left turns will provide an overall benefit. While the level of service or
delay would not improve, the new lane alignment would provide for better lane balance and a better
alignment of traffic northbound across CSAH 30. As traffic increases, it is expected that during the
largest peak in the AM, traffic may not clear the side road in one signal cycle.
Intersection Improvement Considerations:
Based on assessment of safety and operation, extending the eastbound left turn lane to reduce the
potential for high speed read end collisions due to traffic extending past the turn lane is a strong
consideration.
Changes to the intersection to provide northbound and southbound exclusive left turn lanes and the
appropriate left turn phasing is the best long term configuration. This change would require left turn
lanes on Braddock Trail in each direction. Due to the high volume of right turns from the high school, a
new right turn lane for southbound traffic would need to be constructed to create a separate
southbound through lane. While such improvements would provide clear times for left turning traffic
and would allow shared northbound through/right turn traffic to use the right most lane, overall the
intersection operation would only marginally improve during the morning peak time. The safety and
operation review does not indicate an immediate need for change. Provided the traffic volumes stay
consistent along Braddock Trail and no safety issues arise, planning for this modification as a long-term
change when the signal is replaced in approximately the next five to ten years would be applicable.
Recommendation Summary: The following is recommended for improvements.
1. Short Term (2017 CIP) – extend the eastbound left turn lane to provide additional storage for
traffic. Currently, this high volume movement during the morning, when school is in session,
can extend into the through lane. This project to create additional storage will reduce the
potential of rear-end collisions along this high speed roadway.
\\Fs5\pdev1\Highway\Traffic\Studies\CSAH 30\CSAH 30 and Braddock Trl observation and safety summary.docx
2. Longer Term – Side road modifications to create a southbound exclusive lane and new left turn
operation for Braddock Trail. While the change will not specifically improve delay, it will create
a more standard approach for side road turning and crossing movements which could be
helpful, particularly in the morning when school is in session. The signal was installed in 1993.
Based on review of the signal system and extent of this project work, completing these
modifications with the signal replacement would be the most efficient and cost effective
approach. Timing of a potential project also needs to be considered along with other safety and
operational needs of the city and county for resources.
Project would include:
• Add an exclusive southbound right turn lane.
• Reconfigure Braddock Trail to have a separate southbound right, through and left turn
lanes.
• Change pavement markings and signing for the northbound approach to have a separate
left turn and shared through/ right turn lane.
• The improvement would require the City to work with ISD 196 regarding right of way.
• The project would entail the geometric changes to the right turn lane and relocation of the
northwest pole to accommodate the new lane.
• Signal revision to include protective or permissive left turns on Braddock Trail would also be
part of the project scope to provide for flexibility with timing, consistent lane designations
for the side road to best meet driver expectation long term and provide for a better lane
balance based on traffic turns.
• Upgrade signal to ADA standards for pedestrian safety and mobility.