Notes from the Field: Evidence-Based Practices
Using Data to Drive Down Traffic Fatalities
Sergeant James Williams, Metro Nashville Police Department, Tennessee
February 15, 2019
With more than 7.2 million police-reported motor vehicle crashes in 2016, the likelihood that a police officer in the United States will respond to a crash on any given shift is relatively high. Traffic crashes have widespread and varied impacts, ranging from property damage to medical costs and lost productivity. Traffic crashes have killed at least 29,000 people annually since 2007 and injured millions. Despite this harm, there is a dearth of criminal justice research on how police can reduce crashes and their associated harms. When officers complete crash reports, they generate data that can and should be harnessed to develop intervention strategies to reduce crashes and their associated harms.
In recent years there has been an increased interest in implementing evidence-based practices in policing. The emphasis on data analysis, research, and experimentation in other aspects of criminal justice can also be applied to traffic safety initiatives. For example, High Visibility Enforcement (HVE) in crash hot spots has the potential to reduce crashes in those spots. Evidence suggests that traffic enforcement can lead to reductions in crashes, injuries, and fatalities, but for enforcement to be effective, the public must perceive that they will likely be caught if they commit a violation. To create this perception, enforcement efforts generally have to be sustained and overt.
About "Notes from the Field"
NIJ has launched the “Notes from the Field” series to allow leading voices in the field to share their strategies for responding to the most pressing issues on America’s streets today.
In Nashville, we’ve used this evidence to inform our traffic interventions, with promising results. In early 2017, the South Precinct of the Metro Nashville Police Department was struggling with high numbers of motor vehicle crashes that strained our limited resources, prompting us to make a concerted effort to delve into traffic crash data and use that data to develop a strategy to reduce crashes in target areas. During the data collection process, we discovered internal “blind spots” in our data, so we requested additional data from the Tennessee Highway Patrol to overcome these data shortfalls. By using data collected from various sources, a clearer picture of the crash problem emerged. We analyzed crash data including the locations, times, severity, and contributing factors, as well as traffic volume. This analysis then informed the development of an HVE campaign along a main traffic corridor in the precinct.
The HVE plan deployed a group of officers along target areas for two hours leading up to the afternoon rush hour, two days a week, one week a month. Officers were instructed to seek out and enforce only violations that correlated to the factors discovered in the data analysis to contribute to crashes. This shifted the officers’ emphasis away from the number of traffic stops made or tickets issued, and toward specific risk behaviors that could lead to a crash. Briefings were conducted after each operational period to collect data on the types of violations officers observed and citations issued, as well as to discuss problems and areas for improvement.
As a result of the program, traffic crashes dropped significantly in the target areas, even while crashes citywide continued to rise. Analysts found that the HVE operations reduced crashes in the area for a period of about three weeks following an operation, after which crash numbers would begin to increase again. Discovering this “dosage” during the operation allowed us to implement an efficient plan to reduce crashes. A cost-benefit analysis of the plan found that the reduction in crashes relieved officers of a significant amount of time they had previously spent responding to crashes, allowing them to engage in other activities.
The implications of these evaluation findings could lead to a new strategy to combat crashes and plan enforcement efforts. In this case, the analysis of the results of the enforcement efforts was just as important as the data analysis that informed the program. The enforcement dosage we discovered allowed for efforts in a particular crash hot spot to be improved and made as efficient as possible. Analysis in other areas will need to be completed and further experimentation done to see what enforcement dosage, if any, could be deployed in other hot spots.
This program could be scaled to any number of crash hot spots. In a rural setting or an area with low traffic volume, the minimum effective enforcement dosage may not be as frequent. Within a jurisdiction, some trial and error may be needed to understand what works best in each area. However, once optimal intervals for enforcement are discovered, a schedule can be developed for enforcement teams to focus on hot spots to optimize the use of their time and have the greatest safety impact. Ultimately, a change from random, sporadic enforcement to more focused, data-driven, and committed enforcement can lead to meaningful crash reductions.
About “Notes from the Field”
The National Institute of Justice (NIJ) is the research, development, and evaluation arm of the U.S. Department of Justice. NIJ aims to address the critical questions of the criminal justice field, particularly at the state and local levels.
NIJ Director David Muhlhausen developed the “Notes from the Field” series to allow leading voices in the field to share their strategies for responding to the most pressing issues on America’s streets today.
“Notes from the Field” is not a research-based publication. Instead, it presents lessons learned by law enforcement executives and other on-the-ground leaders, from years of experience and thinking deeply about law enforcement issues.
About the Author
Sergeant James Williams is the supervisor of the Metropolitan Nashville Police Department’s DUI Enforcement Unit. During his time with the department, he has served as an officer in patrol, crash investigator and reconstructionist, and patrol supervisor. In his current position, Sergeant Williams is responsible for analyzing crash and arrest data pertaining to driver impairment and developing intervention strategies. He also supervises the investigation of crashes involving life-threatening injuries and fatalities. Sergeant Williams has a bachelor’s degree in sociology from the University of Kentucky and a master’s degree in public policy and administration from Northwestern University. For his master’s thesis, Sergeant Williams researched the use and effectiveness of predictive analytics to inform enforcement strategies aimed at reducing traffic-related deaths and offenses.
Writing and editorial support was provided by Rianna P. Starheim, a writer on assignment at the National Institute of Justice.
[note 1] National Center for Statistics and Analysis. Summary of Motor Vehicle Crashes: 2016 Data. Washington, DC: National Highway Traffic Safety Administration. September 2018.
[note 2] Nicholas Corsaro, Daniel W. Gerard, Robin S. Engel, and John E. Eck. “Not by Accident: An Analytical Approach to Traffic Crash Harm Reduction.” Journal of Criminal Justice 40 no. 6 (2012): 502-514.
[note 3] Bryan Porter. Handbook of Traffic Psychology. Academic Press, 2011.
Date Created: February 15, 2019