Knowledge Resources

In Scottsdale, Arizona, a nine month speed enforcement camera demonstration program (SEP) began in 2006 on a 7.8 mile segment of the SR 101 freeway. While fixed site photo enforcement programs are not uncommon on arterials, this program may have been the first to be deployed on a freeway. This study was conducted to estimate the impact of the SEP on traffic safety, speed, speeding behavior, and daily travel time uncertainty. More specifically, the objectives were to estimate: the impact of the SEP on speeding behavior; the changes in mean speed due to the SEP; the impact of the SEP on traffic safety in the enforcement zone; the total travel time impacts; and the economic impacts of the safety effects. An evaluation estimated the safety and mobility effects of the speed-enforcement program by conducting statistical analyses of crash and crash cost data, traffic data (volumes, travel times, average speeds, and speeding behavior), and economic factors.

METHODOLOGY

This study was conducted to estimate the impact of the SEP on traffic safety, speed, speeding behavior, and daily travel time uncertainty. More specifically, the objectives were to estimate: the impact of the SEP on speeding behavior; the changes in mean speed due to the SEP; the impact of the SEP on traffic safety in the enforcement zone; the total travel time impacts; and the economic impacts of the safety effects.

Five time periods are referenced in the analysis.

• Before (2001 – 2005: various period)
• Warning (01/22/06 – 02/21/06)
• Program (02/22/06 – 10/23/06)
• After (10/24/06 – 12/03/06)
• Reactivation (02/22/07 – 06/29/07)

A microscopic traffic simulation tool, which models the acceleration and speed choice behavior of individual vehicles in detail, was calibrated for the Loop 101 section and used to capture the effects under numerous traffic conditions.

FINDINGS

• The program reduced the average speed by about 9 mph and reduced the speed distribution, factors which are likely to improve safety.
• The speed-enforcement program reduced the number of speeding drivers by at least a 67.5 percent decrease in the proportion of the number of faster drivers, although travel time reliability remained the same.
• The results of a microscopic traffic simulation estimated that the speed-enforcement program resulted in an average of 569 vehicle hours/year and travel time savings of $20,040 (assuming one lane blockage crashes and a $15/hour value) to 37,981 vehicle hours/year and travel time savings of $901,200 (assuming two lane blockage crashes and a $20/hour value).
• The estimates of the total benefits considering the costs of crashes only, range from $16.5 million to $17.1 million per year, depending on the analysis.