Study Finds Photo Enforcement Makes Scottsdale Streets Safer

Making Scottsdale Streets Safer

Photo enforcement has been in use in Scottsdale since 1996, so years of data exist to determine if it actually makes Scottsdale streets safer.  According to a recent study, it does. 

Lee Engineering, an independent firm specializing in research and forensic traffic engineering, analyzed crash data from 2007 to 2013 at 13 intersections and 6 street segments in Scottsdale with photo enforcement and found that crashes were significantly reduced. 

“We wanted to know whether we should continue to use photo enforcement.  This data and its analysis tell us we should,” said Paul Basha, Scottsdale Transportation Director. “ It makes our city streets safer.” 

Lee Engineering analyzed up to five years of data from before and after photo enforcement was implemented.  Noteworthy results from the study include the following:

At the 13 intersections with red light and speeding photo enforcement, overall crashes were reduced by 23 to 24 percent, and crashes related specifically to red-light running were reduced by 33 to 35 percent. 

For the six road segments with speed photo enforcement, overall crashes were reduced by 37 percent. 

At intersections with enforced left-turn movements, left-turn crashes were reduced by 63 percent. 

Both enforced and control locations saw a reduction in crashes, likely due to a positive spillover effect on driver behavior in surrounding areas. 

In 2007 red light and speed photo enforcement was implemented at southbound Scottsdale Road and Shea Boulevard, resulting in a 28 percent reduction in the average number of crashes per year. ( Photo enforcement was chosen for this location because in 2006 there had been 46 accidents at the intersection, and it had the third highest collision rate in the city.) 

The study adds to a growing body of research conducted both in the Valley and nationwide that has shown the effectiveness of photo enforcement for reducing traffic violations and crashes. 

This study, in particular, attempted to address some of the challenges to analyzing photo enforcement programs, such as small data sample sizes.  Lee Engineering used two statistical analyses known as the Wilcoxon Signed-Rank test and the Mann-Whitney U that work with smaller data sets. 

Adding to the robustness of the study, nine of the locations with photo enforcement had a full five years of crash data from before and after implementation.  Data was also available for corresponding control segments and intersections that had similar traffic control, lane configuration and traffic volumes, which further validate that the reduction in crashes wasn’t due to other influences besides photo enforcement. 

Not only does photo enforcement improve safety, it also saves taxpayer money.  A 2005 study done by the Arizona Department of Transportation (Report No.  FHWA-AZ-05-550) of red light camera use by Phoenix and Scottsdale estimated that the reduced number of severe crashes resulted in $4,504 annual savings for the 10 Phoenix intersections studied and $684,134 annual savings for the 14 Scottsdale intersections studied. 

Scottsdale plans a second phase to its study that will look at photo enforcement activated prior to 2007.  It will take longer to compile as the records aren’t as complete related to where signals, left turn arrows and through lanes were located. 
“It’s more complicated to analyze older data,” said Basha. “ But we want to investigate more data to either verify or dispute what we have discovered in this first phase of the study.”