Benefit

In Scottsdale, Arizona, a speed enforcement camera demonstration program on a freeway decreased the number of target crashes by 44 to 54 percent, injury crashes by 28 to 48 percent, and Proptery Damage Only crashes by 46 to 56 percent.

Impact of an automatic speed enforcement program on Loop 101 Freeway in Arizona.


November, 2007
Scottsdale; Arizona; United States


Summary Information

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)
The safety analysis consists of three different evaluation methodologies: a before-and-after (BA) analysis with a comparison group (the comparison site is used to estimate changes in safety from the before to after periods), a BA analysis with a traffic flow correction (crashes are assumed to be proportional to traffic volumes), and a state-of-the-practice empirical Bayes’ BA analysis that corrects for traffic volumes, time trends, and regression-to-the-mean.

FINDINGS

The crash data analysis indicated that the speed-enforcement program was effective in improving overall crash risk in the enforcement zone, although the effect on rear-end crashes is uncertain.
  • The analysis indicated that the program decreased the total number of target crashes by 44 to 54 percent,
  • The total number of injury crashes decreased by 28 to 48 percent.
  • The Property Damage Only crashes decreased by 46 to 56 percent. (The range is attributable to the different analytical methods used in the evaluation.)

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Source

Evaluation of the City of Scottsdale Loop 101 Photo Enforcement Demonstration Program: Final Report AZ-684

Author: Washington, S., Shin, K., and Schalkwyck, I.

Source Date: November, 2007

URL: http://www.azdot.gov/TPD/ATRC/publications/project_reports/PDF/AZ684.pdf

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Goal Areas

Safety

Related Metropolitan Integration Links

Link 13: Freeway Management to Incident Management

Typical Deployment Locations

Statewide

Keywords

photo enforcement, speed cameras, automated speed enforcement, automated enforcement, photo radar

Benefit ID: 2011-00734