Does Heavier Policing Make Roads Safer?
Past research has presented conflicting evidence regarding the efficacy of police presence to maintain road safety. While some studies demonstrate that more police activity leads to better behavior on the roads, others reveal no such association.
Some research has found that police activity on the road increases road safety—but only to an extent, and usually relating only to drunk driving. A ten percent increase in DUI arrests was associated with a one- to two-percent reduction in drunk driving crashes, all other factors accounted for.1 Other studies have failed to establish an association at all, finding no evidence that increased traffic enforcement reduces the incidence of crime, driving violations, or accidents, nor that punishment for particular violations has any effect on rates of offending.2
What’s more, another study argues that traffic ticket issuance has a clear economic motive: for every 10 percent decrease in a municipality’s revenue, traffic ticket issuance in that municipality increases by about 6.4 percent,3 and remains elevated even after revenue increases again. With such a tenuous connection between traffic enforcement and good driving behavior, what’s the purpose of ticketing in the first place?
The data science team at Insurify delved further into the relationship between traffic safety and police forces, referring to their database and to external sources.
This analysis found no relationship between the density of police officers, the rate of enforcement for driving offenses, and traffic fatalities. In this examination, it was neither the case that states with higher levels of traffic violations and vehicle deaths were assigned larger relative police populations, nor that states with more enforcement see fewer deaths. No significant correlations between these factors were identified.
- National averages. Across all states, the average density of police officers is 31.95 officers per 10,000 drivers, while the average overall infraction rate is 1,534 motorists with at least one traffic offense per 10,000 licensed drivers. Additionally, traffic fatalities across all states average to 1.65 deaths per 10,000 licensed drivers.
- Highs and lows. Not all states are equal in terms of police density, driving infractions, and traffic fatalities. New York, North Dakota, and Mississippi have the highest share of police officers, driving offenses, and traffic fatalities, respectively. For every 10,000 drivers, there are 55.69 police officers in NY, 2,597 infractions in ND, and 3.36 traffic fatalities in MS. Conversely, Alabama, Connecticut, and Massachusetts have the lowest shares. In a population of 10,000 drivers, AL has 13.56 police officers, CT has 1,003 infractions, and MA has 0.71 traffic fatalities per 10,000 drivers.
- How safe are America’s roads today? While it’s impossible to attribute changes in road safety to one factor in particular, there’s no question that vehicle safety features have improved from one year to the next. From rearview cameras to lane-keeping assist features to improved crumple zones, each car’s new model year is generally a safer version of the last. For decades, from the 1960s to the turn of the 21stcentury, traffic fatality rates were consistent with this trend in vehicle safety, decreasing from 5.04 deaths per 10,000 licensed drivers in 1966 to 1.53 deaths per 10,000 licensed drivers in 2014. Since then, however, fatality rates have begun to climb despite continued improvements to vehicle safety.
To determine the relationship between traffic incidents and police officers by state, the data and research team at Insurify conducted a correlational study analyzing the density of police officers, frequency of traffic fatalities, and rate of traffic violations by state.
The density of police officers by state, defined as the proportion of police officers in that state in comparison to licensed drivers, was calculated using data published by the Federal Bureau of Investigation (FBI) and the Bureau of Transportation Statistics. Law enforcement data were gathered from the FBI’s latest Uniform Crime Reporting statistics, which list the number of police officers in each state. These numbers were compared against the most recent driver data released by the Bureau of Transportation Statistics, which detail the number of licensed drivers in each state, yielding the density of police officers by state.
Infraction rates by state were calculated using data from Insurify’s database of over 2 million insurance applications. Drivers disclose personal and vehicle information in addition to driving history, including past accidents and driving infractions. Infractions were sorted into seven categories: license-based moving violations, insurance-based moving violations, speeding violations, signal violations, passing violations, DUIs, and reckless driving violations. For each state, Insurify’s data scientists calculated the proportion of drivers with these violations on their record. Infraction rates by state were compared with the density of police officers by state, to determine any correlation between the two.
The latest state-based traffic fatality statistics on rates of traffic deaths per licensed driver and per million miles traveled were gathered from the State Traffic Data report, released by the National Highway Traffic Safety Administration (NHTSA). Traffic fatality rates were also compared with the density of police officers by state and with statewide infraction rates, to determine any relationship between the density of law enforcement officers, the rate at which drivers are charged with driving offenses, and traffic safety outcomes.
Correlations Between Police Presence, Rates of Driving Offenses, and Traffic Fatalities
Police Officers and Driving Offenses
This table illustrates the statistical relationship between the density of police officers and rates of driving offenses by state. Driving offenses are listed in order of the frequency in which they occur.
|Driving Infraction x Police Officer Density||R-Value||Strength and Direction of Correlation||P-Value|
|All Infractions x Police Officer Density||r=-0.296||Moderate Negative Correlation||p=0.037|
|Speeding Infractions x Police Officer Density||r=-0.245||Negligible Correlation||p=.087|
|License Infractions x Police Officer Density||r=-0.257||Negligible Correlation||p=0.071|
|Signal Infractions x Police Officer Density||r=0.148||Negligible Correlation||p=0.304|
|DUIs x Police Officer Density||r=-0.271||Negligible Correlation||p=0.057|
|Reckless Driving x Police Officer Density||r=-0.046||Negligible Correlation||p=0.751|
|<Insurance-related Infractions x Police Officer Density||r=-0.347||Moderate Negative Correlation||p=0.014|
|Passing Violations x Police Officer Density||r=-0.018||Negligible Correlation||p=0.899|
Only two driving offenses have a statistically significant correlation with police officer density. Insurance-related infractions have a moderate negative correlation with police officer density, r=-0.35, while driving infractions, when grouped as a whole and compared with police officer density, also reveal a moderate negative correlation, r=-0.35. All other driving infractions by state, considered separately, are not correlated with police officer density by state.
Police Officers and Traffic Fatalities
This table illustrates the statistical relationship between the density of police officers by state and traffic fatality rates by state.
|Traffic Fatality Rate||R-Value||Strength and Direction of Correlation||P-Value|
|Traffic Fatalities per State Population x Police Officer Density||r=0.156||Negligible Correlation||p=0.140|
|Traffic Fatalities per Licensed Driver x Police Officer Density||r=-0.280||Moderate Negative Correlation||p=0.049|
|Traffic Fatalities per Miles Driven x Police Officer Density||r=0.133||Negligible Correlation||p=0.359|
A statistical analysis of the relationship between police officer density and traffic fatality rates by state reveals no significant correlation between the two. Simply put, the numbers suggest that traffic fatalities are independent of law enforcement’s presence on the roads, at least on a state-by-state basis.
Traffic Fatalities and Driving Offenses
This table illustrates the statistical relationship between traffic fatality rates by state and driving offenses by state. Driving offenses are listed in order of the frequency in which they occur.
|Driving Infraction x Traffic Fatalities per Licensed Driver||R-Value||Strength and Direction of Correlation||P-Value|
|All Infractions x Fatalities per Licensed Driver||r=0.053||Negligible Correlation||p=0.716|
|Speeding Infractions x Fatalities per Licensed Driver||r=0.022||Negligible Correlation||p=0.882|
|License Violations x Fatalities per Licensed Driver||r=-0.006||Negligible Correlation||p=0.967|
|Signal Violations x Fatalities per Licensed Driver||r=-0.305||Moderate Negative Correlation||p=0.031|
|DUIs x Fatalities per Licensed Driver||r=0.109||Negligible Correlation||p=0.450|
|Reckless Driving x Fatalities per Licensed Driver||r=-0.020||Negligible Correlation||p=0.891|
|Insurance-related Infractions x Fatalities per Licensed Driver||r=0.254||Negligible Correlation||p=0.075|
|Passing Violations x Fatalities per Licensed Driver||r=-0.417||Moderate Negative Correlation||p=0.003|
Conclusion: Limitations and Avenues for Future Research
While Insurify’s study of nationwide figures on policing and traffic safety found no notable correlations between the ratio of law enforcement officers to drivers, the rate at which drivers are convicted of moving violations, and the number of annual motor vehicle fatalities, this is just a preliminary analysis. With the intent to initiate wider conversations about the outcomes of policing on our roads as well as in our cities, we acknowledge the need for additional research on this subject matter. Here is a sample of the limits inherent in this study as well as future research directions that could clarify the relationship between officers, the laws they enforce, and public safety.
- This is not a longitudinal study. This analysis does not examine the impact police have on the number of drivers charged with traffic incidents nor the number of lives lost on the road over time. A longitudinal study, especially one conducted over a more local scale, may identify that a higher density of police translates either to fewer traffic incidents through deterrence or to higher citation rates due to heavier enforcement. Conversely, a study that sampled these figures over time and still found no relationship would bolster the preliminary conclusions of this examination.
- Not all officers police the roads. Law enforcement in the United States is a broad term under which a range of occupations exists. While this study distinguishes between law enforcement officers and police officers to include only police in its statistical analysis, a police officer’s time may not be spent enforcing only traffic laws.
- Not all drivers are licensed. Many drivers in the United States do not own a valid license and consequently are not included in the Bureau of Transportation Statistics’ state-by-state count of licensed drivers. Three percent of all drivers in the United States are unlicensed, according to the AAA Foundation for Traffic Safety, but there may be fluctuations in this percentage by state. This would result in a high or low skew of a state’s police officer density, depending on the share of unlicensed drivers in that state.
- Traffic outcomes go beyond fatalities. While the number of annual vehicle-related deaths is, without question, one of the most pressing measures of traffic safety, it’s not the only one. This study did not investigate the impact of policing on other relevant outcomes including crash-related injuries and property damage.
Policing The Drunk Driving Problem: A Longitudinal Examination of DUI Enforcement and Alcohol Related Crashes in the U.S. (1985–2015); Effects of enforcement intensity on alcohol impaired driving crashes
The effects of aggressive policing: The Dayton traffic enforcement experiment; Ahlin, E. M., Zador, P. L., R. First-time DWI offenders are at risk of recidivating regardless of sanctions imposed
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