Law enforcement’s impact on our lives is at the forefront of national conversation following protests across America. With this in mind, we look to law enforcement’s role on America’s roads.
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.
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.
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.
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.
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|
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.
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
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