Salt 2014 Salt Lake City TACT Enforcement Evaluation Report

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SALT LAKE CITY TACT EVALUATION September 25, 2014

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Salt Lake City TACT Evaluation Report The goal of the SLC TACT project is to reduce unsafe behaviors and decrease crashes between

passenger and commercial vehicles. The SLC TACT intervention consisted of concentrated

media and increased enforcement over a three week period in April 2014 to encourage passenger

and commercial vehicle drivers to travel safely around one another within the city limits. Based

on data analyzed during Phase I of the project, the SLC TACT intervention focused on four

targeted behaviors for drivers of both passenger and commercial vehicles: 1) failing to yield the

right-of-way, 2) disregarding traffic signals, 3) improper turn, and 4) following too closely. The

evaluation of the media efforts are detailed in a different report.

This report concentrates on the evaluation of driver behaviors using observational, citations for

the targeted behaviors, and motor vehicle crash data. Below we describe the purpose, data, and

the key findings for each of the three areas. Observational Data

Purpose: To directly assess driving behaviors pre and post the TACT intervention, we collected information on the frequency of negative interactions occur between passenger and commercial

vehicles in Salt Lake City pre and post the TACT enforcement period.

Data Collection: Trained observers, using a standardized data collection form, collected data on negative passenger and commercial vehicle driver interactions at designated intersections in Salt

Lake City. We collected data 3 weeks prior to the TACT enforcement period and 3 weeks post

TACT enforcement. All observers received classroom and field training (Please see Appendix 1

for the observational data collection protocol). We selected the intersections according to data

received from Salt Lake City Police Department and Utah Department of Transportation. These

sites were determined to have a high rate of commercial vehicle travel and passenger and

commercial vehicle crashes, while also providing a safe location from which to accurately

observe commercial and passenger driver interactions.


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The sites selected were

21South /9West-observations will occur at a large intersection with nearby truck stop

21South /7East-observations will occur at an intersection and mid-block locations

6North/4West- observations will occur at an intersection and mid-block locations

Because some of the targeted interactions (e.g., disregarding traffic signals and improper turns)

were more likely to occur at an intersection, while other interactions (e.g., following too closely)

were more likely to occur mid-block, observations were collected from both types of locations.

Mid-block observations were not conducted at the 21 South/9 West location due to a

combination of construction and a lack of safe observation locations.

Key Findings: As seen in Table 1, we conducted 48-observation shifts pre-enforcement and 67-

post enforcement. While the number of observation shifts differed between the time periods,

there was no difference between the rate of commercial vehicles observed per shift between the

pre- and post-enforcement periods (83 vs. 84, p = 0.953). Please see Appendix 2 for commercial

vehicle counts by location.

Table 1. SLC TACT Observational Commercial Vehicle Count Pre- and Post- TACT Enforcement

Observation Period

Pre-

Enforcement Post-

Enforcement Pooled T-test

P-value Commercial Vehicle Count

Number of Observation Shifts 48 67

Sum 3990 5630

Mean (SD) 83 (81.9) 84 (80.4) 0.953


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Below is a comparison of the rate of observed negative interactions by vehicle type pre and post

TACT Enforcement by location. Table 2 shows the rate of overall total negative interactions

decreased by almost half after the TACT intervention. The largest decrease was seen in

following too close and improper turns for both commercial and passenger vehicle drivers. This

same pattern was observed at each location.

Table 2. SLC TACT Negative Interaction Rate by Vehicle Type from Observational Data Collected Pre- and Post-TACT Enforcement Period

Commercial Vehicles Passenger Vehicles

Interaction Type Pre Post Diff Pre Post Diff

All Locations

Total Interactions 2.31 1.30 -1.011 1.96 0.58 -1.381

Disregarding Traffic Signals 0.81 0.69 -0.13 0.29 0.16 -0.13

Improper Turns 0.56 0.19 -0.37 0.19 0.00 -0.19

Failure to Yield 0.21 0.10 -0.10 0.06 0.03 -0.03

Following Too Close 0.54 0.27 -0.27 1.40 0.31 -1.081

Other 0.19 0.04 -0.14 0.02 0.07 0.05

2100 S 900 W


Disregarding Traffic Signals 0.63 0.52 -0.10 0.29 0.10 -0.19

Improper Turns 0.52 0.13 -0.391 0.19 0.00 -0.19

Failure to Yield 0.13 0.07 -0.05 0.04 0.01 -0.03

Following Too Close 0.44 0.13 -0.30 1.02 0.19 -0.831

Other 0.13 0.03 -0.10 0.02 0.04 0.02

2100 S 700 E


Disregarding Traffic Signals 0.04 0.03 -0.01 0.00 0.01 0.01

Improper Turns 0.02 0.01 -0.01 - - -

Following Too Close 0.02 0.03 0.01 0.19 0.01 -0.17

Other 0.04 0.00 -0.04 - - -


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Table 2. SLC TACT Negative Interaction Rate by Vehicle Type from Observational Data Collected Pre- and Post-TACT Enforcement Period

Commercial Vehicles Passenger Vehicles

Interaction Type Pre Post Diff Pre Post Diff

600 N 400 W


Disregarding Traffic Signals 0.15 0.13 -0.01 0.00 0.04 0.04

Improper Turns 0.02 0.04 0.02 - - -

Failure to Yield 0.08 0.03 -0.05 0.02 0.01 -0.01

Following Too Close 0.08 0.10 0.02 0.19 0.10 -0.08

Other 0.02 0.01 -0.01 0.00 0.03 0.03 1Significant reduction in negative interactions (p < 0.05). Rates are calculated as Negative Interactions observed per Observation Shift

The observational data show that there was a significant reduction between the rate of negative

interactions at each location between the pre- and post-TACT intervention time periods. The

greatest decrease was observed in the rate of following too close. The decrease in the rate of total

negative interactions following the TACT enforcement period suggests that the TACT

intervention positively affected driver behavior.

Targeted Behavior-Related Citations

Purpose: To assess the results of increased high visibility and awareness of the TACT

enforcement, daily counts of citations and warnings for the target behavior categories were

analyzed. A combined high visibility enforcement and awareness campaign was used alert the

public of the importance of decreasing risky driving practices around commercial vehicles.

Police officers reinforced the media messages with targeted enforcement and increased warnings

to passenger and commercial vehicle drivers when any of the four-targeted behaviors were

observed during the intervention period.


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Data Collection: Citation data were obtained from two sources. Citations data for the four-

targeted behaviors from the Salt Lake City Police Department Record Management System for

the years 2012-2014 are presented in Figure 1. Comparing data from the same time period from

previous years allowed us to control for any temporal trends that may exist outside of the TACT

intervention. Data for Figure 2 were obtained from the Salt Lake City Police Traffic

Enforcement Section. This section tracked the citations and warnings issued during the TACT

enforcement period.

Key Findings: Figure 1 shows the comparison of citations issued by day for the first six months

of the years 2012 to 2014. The high visibility enforcement period is delineated with vertical bars

so that the rates between the pre-enforcement, enforcement, and post-enforcement periods can be

compared across years. We found that citations remained relatively constant over the six month

time period with more citations issued in 2012 compared to 2013 and 2014. The data for the

TACT enforcement period in 2014 shows an increase in the number of citations issued at the end

of the enforcement period. Because the high visibility campaign involved both issuing citations

and warnings, we obtained data from the Salt Lake City Traffic Enforcement Unit, which tracks

both of these activities.


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Figure 2 shows that there was sustained enforcement throughout the TACT period (showing

there were 40 to 50 warnings and citations issued per day) with police officers issuing more

warnings than citations in the beginning of the time period with a reversal at the end of the

period.


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While the total number of citations issued during the high visibility enforcement period remained

similar to previous years, the combined use of warnings and citations during the TACT

intervention period appears to have had a positive impact on driving behavior as demonstrated by

the decrease in negative interactions observed in the post-TACT intervention period. While we

cannot directly associate the issuing of warnings and citations with the decrease in negative

interactions, it is interesting to note that shortly after the TACT-enforcement period there is an

overall decrease in the number of citations issued that overlaps with the decrease in negative

interactions observed at our three locations.

Motor Vehicle Crash Data

Purpose: To assess the impact of the TACT enforcement on the number of crashes between

commercial and passenger drivers.

Data Collection: Data were obtained on motor vehicle traffic crashes involving a commercial

vehicle from the Salt Lake City Police Department Record Management System for the years

2012-2014 to control for any temporal trends that may exist outside of the TACT intervention.


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Key Findings: While it is expected the number of commercial vehicle crashes during the TACT

study period will decrease, it is unlikely that we will be able to demonstrate statistical

significance due to the relative rareness of these events.

Table 3 below shows the counts of commercial vehicle crashes that occurred before, during and

after the TACT intervention window dates in each year. The counts display a considerable

amount of variability and do not clearly indicate an identifiable trend.

Table 3. SLC TACT Crashes Involving a Commercial Vehicle by Enforcement Time Period and Year

Year

2012

(N = 12) 2013

(N = 34) 2014

(N = 20)

Time Period

Pre-Enforcement (Jan/1-Mar/14) 4 (33.3%) 30 (88.2%) 13 (65.0%)

Enforcement (Mar/15-Apr/18) 5 (41.7%) 2 (5.9%) 2 (10.0%)

Post-Enforcement (Apr/19-Jun/30) 3 (25.0%) 2 (5.9%) 5 (25.0%)

Crashes exclude Public Transit, School Buses and single vehicle collisions. Year= January through June of each year

Table 4 displays a summary of the characteristics of drivers involved in commercial vehicle crashes. Except for commercial drivers in 2012, the three years showed similar results in driver gender. Driver age was similar in all three years. Notably, the proportion of passenger and commercial drivers that contributed to the crashes is also roughly equal for all three years. Additionally, most crashes resulted in no or minor injuries.


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Table 4. SLC TACT Crash Driver Characteristic Summary by Year

Year

2012 2013 2014

Passenger Commercial Passenger Commercial Passenger Commercial

N 13 13 33 36 20 18

Sex

Female 3 (23.1%) 9 (69.2%) 8 (24.2%) 0 (0.0%) 8 (40.0%) 0 (0.0%)

Male 10 (76.9%) 4 (30.8%) 25 (75.8%) 36 (100.0%) 12 (60.0%) 18 (100.0%)

Age

Min, Max 23, 61 22, 73 19, 89 23, 66 20, 74 22, 71

Median [Q1, Q3] 41 [35, 50] 33 [23, 38] 43 [31, 59] 43 [34, 51] 42 [32, 58] 42 [30, 48]

Driver Contributed

Contributed to Crash 5 (38.5%) 7 (53.8%) 18 (54.5%) 18 (50.0%) 12 (60.0%) 10 (55.6%)

Injury Type

No Injury 11 (84.6%) 5 (38.5%) 25 (75.8%) 32 (88.9%) 19 (95.0%) 15 (83.3%)

Possible Injury 2 (15.4%) 2 (15.4%) 2 (6.1%) 1 (2.8%) 1 (5.0%) 2 (11.1%)

Non-Incapacitating Injury

0 (0.0%) 5 (38.5%) 4 (12.1%) 0 (0.0%) 0 (0.0%) 1 (5.6%)

Incapacitating Injury

0 (0.0%) 1 (7.7%) 1 (3.0%) 1 (2.8%) 0 (0.0%) 0 (0.0%)

Unknown 0 (0.0%) 0 (0.0%) 1 (3.0%) 2 (5.6%) 0 (0.0%) 0 (0.0%)

Crashes exclude Public Transit, School Buses and single vehicle collisions.

As expected no statistically significant associations could be identified from the crash data due to

the relatively rare occurrences of commercial vehicle crashes. In 2014, there were only two

commercial vehicle crashes during the high visibility enforcement period, matching the number

observed in the year before but less than half of the number from 2012. Our data show that a

crash between commercial and passenger vehicle drivers continues to primarily involve males


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between the ages of 30 and 50 years suggesting that future high visibility enforcement and media

campaigns be targeted at this demographic.

Conclusions

Our data demonstrates that there was a decrease in negative interactions in the targeted behavior

areas following the TACT intervention. Specifically, we found a significant decrease in the

overall number of negative interactions at each of our three observation locations, with the

greatest decrease being observed in Following Too Close. Salt Lake City police officers issued

between 40 and 50 citations and warnings each day during the high visibility enforcement

period. The increase in citations towards the end of the high visibility enforcement period may

have contributed to the observed decrease in negative interactions and citations issued during the

post-TACT period. While there were not enough crashes to detect any statistical trends that may

exist in the data, we did find that males between the ages of 30 and 50 years continue to make up

the majority of drivers involved in commercial and passenger vehicle crashes. Future efforts

targeting this demographic are likely to have the greatest impact on reducing crashes.


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APPENDIX 1. OBSERVATIONAL PROTOCOL

Introduction The goal of the SLC TACT project is to reduce unsafe behaviors and decrease crashes between

passenger and commercial vehicles. The SLC TACT intervention will consist of concentrated

media and increased enforcement to encourage passenger and commercial vehicle drivers to

travel safely around one another within the city limits. The SLC TACT intervention will focus on

four targeted behaviors for drivers of both passenger and commercial vehicles: 1) failing to yield

the right-of-way, 2) disregarding traffic signals, 3) improper turn, and 4) following too closely.

Media efforts will raise driver awareness by educating passenger and commercial vehicle drivers

about how to safely interact with one another on the roadway and the importance of avoiding the

four targeted behaviors. Police officers will reinforce the media messages and help change driver

behaviors by issuing citations to passenger and commercial vehicle drivers when any of the four

targeted behaviors are observed. In addition, the accuracy and use of citations will increase as

traffic enforcement officers use the NCIC codes when issuing citations.

Study Design This is an observational study design. Data collection will be conducted by two person

observation teams. All observers will receive both classroom and field training. University of

Utah investigators will make unannounced visits to scheduled data collection locations in order

to ensure data are being collected according to the research protocol.

Sample Design We have selected observation sites according to data received from SLC PD and UDOT. These

sites were determined to have the highest rate of commercial vehicle travel and therefore provide

the greatest opportunity for passenger and commercial vehicle interactions.

Analyses will be based on the number of commercial vehicles passing the observation location

during the observation period. We expect an average number of at least 40-250 commercial

vehicles per hour to be observed and an average negative interaction rate of two -10 negative

interactions per hour depending on location. Under these assumptions we will have the at least

80% power to detect a 50% drop in negative interactions following the intervention period.


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Data Collection Site Selection Intersections were selected according to high frequency of commercial vehicle traffic and

passenger and commercial vehicle crashes. Because some of our targeted interactions are more

likely to occur at an intersection, such as disregarding traffic signals and improper turns, while

others are more likely to occur mid-block, such as following too closely, observations will be

collected from both types of locations.

The sites selected are

21S/9W-observations will occur at a large intersection with nearby truck stop

21S/7E-observations will occur at an intersection and mid-block locations

6N/4W- observations will occur at an intersection and mid-block locations

In the event that an original intersection is permanently or temporarily unavailable, due to road

construction, detours, closure, etc. an alternate site will be selected. Observation teams will be

supplied with specified alternate sites to use if needed.

Training We will recruit teams of observers to collect data. Observers will be recruited through the

University of Utah with preference given to individuals who have experience in field data

collection. Observers must be able to stand for long periods of time, work outdoors, and

successfully complete the training program. Observer training will be conducted at University of

Utah Department of Pediatrics.

At the conclusion of the classroom training all data collectors will participate in field training

and be required to complete a sample data collection period. The group will review the results of

the sample data collection period to discuss similarities and differences among the individual

results.

Observation Periods and Quality Control All passenger and commercial vehicle interaction observations will be conducted during

weekdays between 7:00 am and 6:00 pm. The schedule will focus on rush hour (before 9:30 am


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and after 3:30 pm) to increase the amount of commercial vehicle traffic. Data collection will take

place in 45 minute stretches during four hour time blocks.

Observation teams will be supplied with a packet describing the observation location, the

direction to observe, and containing data collection sheets.

Data Collection Forms Data collection will be accomplished by use of a standardized data collection sheet. Observation

teams will document the location, date, time, location type (intersection or mid-block), and any

alternate site or extenuating circumstances when initiating each survey.

Observation teams will observe as many lanes of traffic as they can comfortably monitor while

observing. When observing at a mid-block location, only one direction of traffic will be

observed. However, when observing at an intersection, two directions will be observed as

detailed in the training. One member of the team will be assigned to count all commercial

vehicles passing the observation site while other team members will identify and record all

negative interactions between commercial and passenger vehicles. Data collection will continue

for 45 minutes at which point the collection team will be allotted a 15-minute break. At the

conclusion of the break, team members will switch roles and begin observing for a new 45

minute period. Four 45-minute observation periods will be expected at each location.

Quality Control Procedures The University of Utah investigators will make unannounced QC visits to at least one data

collection site per team. During the regular QC visits, we will evaluate the data collection teams

performance from a distance (if possible), and then work alongside the data collection team. We

will ensure that the data collection team is following the survey protocol including: being on

time at assigned sites, using the appropriate data collection forms, and making accurate

observations of passenger and commercial vehicle interactions.

In the event it is discovered that a data collection team has falsified data, the observation form(s)

will be destroyed and the observation will be duplicated by other trained observers.


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APPENDIX 2. DETAILED INFORMATION ON COMMERCIAL VEHICLE COUNTS BY OBSERVATION LOCATION

2014 SLC TACT Commercial Vehicle Count Summary Comparison by Location and Vehicle Type*

Location

2100 S 900 W 2100 S 700 E 600 N 400 W All Locations

I MB I MB I MB I MB Overall

Pre-Enforcement

Truck Count

Number of Observation Shifts

16

16

8

8

8

8

32

16

48

Sum 3097 3097 154 93 413 233 3664 326 3990

Mean (SD)

194 (25.8)

194 (25.8)

19 (9.1)

12 (6.3)

52 (22.7)

29 (8.7)

115 (83.9)

20 (11.7)

83 (81.9)

Post-Enforcement

Truck Count

Number of Observation Shifts

21

21

11

7

13

15

45

22

67

Sum 4129 4129 222 76 725 478 5076 554 5630

Mean (SD)

197 (25.2)

197 (25.2)

20 (9.4)

11 (4.4)

56 (30.2)

32 (12.3)

113 (83.8)

25 (14.4)

84 (80.4)

* I = Intersection; MB = Mid-Block

IntroductionStudy DesignSample DesignData CollectionSite SelectionTrainingObservation Periods and Quality ControlData Collection Forms

Documents

Salt 2014 Salt Lake City TACT Enforcement Evaluation Report