Effects of vehicle power on passenger vehicle speeds

<p><b>Objectives</b>: During the past 2 decades, there have been large increases in mean horsepower and the mean horsepower-to–vehicle weight ratio for all types of new passenger vehicles in the United States. This study examined the relationship between travel speeds and vehicle power, defined as horsepower per 100 pounds of vehicle weight.</p> <p><b>Methods</b>: Speed cameras measured travel speeds and photographed license plates and drivers of passenger vehicles traveling on roadways in Northern Virginia during daytime off-peak hours in spring 2013. The driver licensing agencies in the District of Columbia, Maryland, and Virginia provided vehicle information numbers (VINs) by matching license plate numbers with vehicle registration records and provided the age, gender, and ZIP code of the registered owner(s). VINs were decoded to obtain the curb weight and horsepower of vehicles. The study focused on 26,659 observed vehicles for which information on horsepower was available and the observed age and gender of drivers matched vehicle registration records. Log-linear regression estimated the effects of vehicle power on mean travel speeds, and logistic regression estimated the effects of vehicle power on the likelihood of a vehicle traveling over the speed limit and more than 10 mph over the limit.</p> <p><b>Results</b>: After controlling for driver characteristics, speed limit, vehicle type, and traffic volume, a 1-unit increase in vehicle power was associated with a 0.7% increase in mean speed, a 2.7% increase in the likelihood of a vehicle exceeding the speed limit by any amount, and an 11.6% increase in the likelihood of a vehicle exceeding the limit by 10 mph. All of these increases were highly significant.</p> <p><b>Conclusions</b>: Speeding persists as a major factor in crashes in the United States. There are indications that travel speeds have increased in recent years. The current findings suggest the trend toward substantially more powerful vehicles may be contributing to higher speeds. Given the strong association between travel speed and crash risk and crash severity, this is cause for concern.</p

Effects of automated speed enforcement in Montgomery County, Maryland, on vehicle speeds, public opinion, and crashes

<p><b>Objectives</b>: In May 2007, Montgomery County, Maryland, implemented an automated speed enforcement program, with cameras allowed on residential streets with speed limits of 35 mph or lower and in school zones. In 2009, the state speed camera law increased the enforcement threshold from 11 to 12 mph over the speed limit and restricted school zone enforcement hours. In 2012, the county began using a corridor approach, in which cameras were periodically moved along the length of a roadway segment. The long-term effects of the speed camera program on travel speeds, public attitudes, and crashes were evaluated.</p> <p><b>Methods</b>: Changes in travel speeds at camera sites from 6 months before the program began to 7½ years after were compared with changes in speeds at control sites in the nearby Virginia counties of Fairfax and Arlington. A telephone survey of Montgomery County drivers was conducted in Fall 2014 to examine attitudes and experiences related to automated speed enforcement. Using data on crashes during 2004–2013, logistic regression models examined the program's effects on the likelihood that a crash involved an incapacitating or fatal injury on camera-eligible roads and on potential spillover roads in Montgomery County, using crashes in Fairfax County on similar roads as controls.</p> <p><b>Results</b>: About 7½ years after the program began, speed cameras were associated with a 10% reduction in mean speeds and a 62% reduction in the likelihood that a vehicle was traveling more than 10 mph above the speed limit at camera sites. When interviewed in Fall 2014, 95% of drivers were aware of the camera program, 62% favored it, and most had received a camera ticket or knew someone else who had. The overall effect of the camera program in its modified form, including both the law change and the corridor approach, was a 39% reduction in the likelihood that a crash resulted in an incapacitating or fatal injury. Speed cameras alone were associated with a 19% reduction in the likelihood that a crash resulted in an incapacitating or fatal injury, the law change was associated with a nonsignificant 8% increase, and the corridor approach provided an additional 30% reduction over and above the cameras.</p> <p><b>Conclusions</b>: This study adds to the evidence that speed cameras can reduce speeding, which can lead to reductions in speeding-related crashes and crashes involving serious injuries or fatalities.</p

Effect of Passenger Presence on Older Drivers’ Risk of Fatal Crash Involvement

<div><p> <b>Objective:</b> To determine the association between passenger presence and risk of fatal crash involvement in relation to driver and passenger age and gender, focusing especially on drivers ages 65 and older.</p> <p> <b>Methods:</b> Data on US fatal crashes were obtained for 2002–2009. Using the quasi-induced exposure methodology, logistic regression analysis was used to predict the odds of fatal crash involvement as a function of driver age and gender as well as passenger age and gender.</p> <p> <b>Results:</b> Overall, risk of fatal crash involvement with passengers was 43 percent lower for drivers ages 65–74 and 38 percent lower for drivers 75 and older. Older drivers’ risk of fatal crash involvement was lower with almost all combinations of passenger age and gender; there was no reduction in risk with passengers ages 75 and older. Effects were stronger at nonintersection locations than at intersection locations.</p> <p> <b>Conclusion:</b> Older drivers’ crash risk is lower with almost every combination of passenger age group and gender. It is unclear whether the presence of passengers lowers older driver crash risk or whether safer drivers tend to ride with passengers.</p> </div

Effects of Washington State’s alcohol ignition interlock laws on DUI recidivism: An update

<p><b>Objective:</b> The objective of this study was to examine the effects of changes to Washington State’s alcohol ignition interlock laws: moving issuance of interlock orders from the courts to the driver licensing department (July 2003); extending the interlock order requirement to all persons convicted of driving under the influence (DUI; June 2004); allowing an interlock in lieu of an administrative driver’s license suspension (January 2009); and requiring proof of interlock installation to reinstate the driver’s license (January 2011).</p> <p><b>Method:</b> Trends in conviction types, interlock installation rates, and 2-year cumulative recidivism rates were examined for first-time and repeat offenders with convictions stemming from DUI arrests during 1999–2012. Autoregressive integrated moving average (ARIMA) models examined the association between law changes and installation rates, law changes and recidivism rates, and installation rates and recidivism rates.</p> <p><b>Results:</b> During the study period, there was a large increase in the proportion of first-time DUI arrests reduced to alcohol-related negligent/reckless driving convictions, offenses not requiring interlock orders. The interlock installation rate increased substantially and the recidivism rate declined substantially among both first and repeat offenders. Based on the ARIMA models for first offenders, the 2004 and 2009 law changes were associated with increased interlock installation rates and lower recidivism rates. For first offenders arrested during the last quarter of 2012, the model estimates a 26% reduction in the recidivism rate (from an expected 7.7% without the 4 laws to 5.6%). A 1 percentage point increase in the interlock installation rate was associated with a 0.06 percentage point decline in the recidivism rate among first offenders. If the association carried forward and if the installation rate had been 100% rather than 38% in the last quarter of 2012, the 2-year recidivism rate would have been reduced from 5.6 to 2%. Among repeat offenders, the 2003 and 2009 law changes were associated with increased interlock installation rates, and the 2009 law change was associated with a nonsignificant decline in recidivism.</p> <p><b>Conclusions:</b> In Washington, rates of interlock installations increased as interlock laws were strengthened, and the increase was associated with reductions in recidivism among first DUI offenders. Washington’s experience suggests that states can reduce DUI recidivism by requiring interlock orders for all offenders, allowing offenders to install interlocks in lieu of an administrative driver’s license suspension, and closing statutory loopholes that allow plea reductions to convictions without interlock orders.</p