Evaluation of the Scottsdale Loop 101 automated speed enforcement demonstration program

doi:10.1016/j.aap.2008.12.011

Accident Analysis & Prevention

Volume 41, Issue 3, May 2009, Pages 393-403

https://doi.org/10.1016/j.aap.2008.12.011 Get rights and content

Abstract

Speeding is recognized as a major contributing factor in traffic crashes. In order to reduce speed-related crashes, the city of Scottsdale, Arizona implemented the first fixed-camera photo speed enforcement program (SEP) on a limited access freeway in the US. The 9-month demonstration program spanning from January 2006 to October 2006 was implemented on a 6.5 mile urban freeway segment of Arizona State Route 101 running through Scottsdale. This paper presents the results of a comprehensive analysis of the impact of the SEP on speeding behavior, crashes, and the economic impact of crashes. The impact on speeding behavior was estimated using generalized least square estimation, in which the observed speeds and the speeding frequencies during the program period were compared to those during other periods. The impact of the SEP on crashes was estimated using 3 evaluation methods: a before-and-after (BA) analysis using a comparison group, a BA analysis with traffic flow correction, and an empirical Bayes BA analysis with time-variant safety. The analysis results reveal that speeding detection frequencies (speeds ≥ 76 mph) increased by a factor of 10.5 after the SEP was (temporarily) terminated. Average speeds in the enforcement zone were reduced by about 9 mph when the SEP was implemented, after accounting for the influence of traffic flow. All crash types were reduced except rear-end crashes, although the estimated magnitude of impact varies across estimation methods (and their corresponding assumptions). When considering Arizona-specific crash related injury costs, the SEP is estimated to yield about $17 million in annual safety benefits.

Introduction

Speeding is recognized as a major contributing factor in traffic crashes. In order to reduce speed-related crashes, the city of Scottsdale, Arizona implemented the first fixed photo speed enforcement camera demonstration program (SEP) in the US on a high-speed limited access facility. The 9-month demonstration program spanning from January 2006 through October 2006 was implemented on a 6.5 mile stretch of Arizona State Route 101, an urban freeway in Scottsdale. The SEP consisted of 6 speed detection stations in the enforcement zone, in which three cameras were positioned to enforce speed for each direction of travel (north and south bound). The speed limit on the SR 101 freeway is 65 mph, while the enforcement equipment is triggered to photograph drivers traveling at speeds of 76 mph or greater. This analysis is focused on estimating:

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The impact of the SEP on citable speeding behavior (i.e.. speeds ≥ 76 mph).
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The impact of the SEP on average speeds.
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The effect of the SEP on traffic safety.
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The expected economic safety benefit of the SEP.

This evaluation, sponsored by the Arizona Department of Transportation (ADOT) and the City of Scottsdale, utilizes data from the Arizona Department of Public Safety (crash reports), ADOT (motor vehicle crashes, traffic volumes, and traffic speeds), the City of Scottsdale (traffic volumes and speeds), RedFlex (speeding detections and traffic speeds), and the Arizona Crash Outcome Data Evaluation System (crash details and crash costs).

Section snippets

Literature review

Numerous studies have been conducted to elucidate the relationship between speed and safety: detailed reviews of which are provided elsewhere (Lave and Lave, 1998, Stuster et al., 1998, Skszek, 2004, Kweon and Kockelman, 2005). In the 1960s, many studies found that the variance of speed is one of the most important factors affecting safety, suggesting a U-shaped relationship between crash rate and variance in speed. The relationship illustrates that the more the speed of driver deviates from

Impact on ticketed speeding behavior

Speed detection data in the enforcement zone are used to analyze the impact of the SEP on ticketed speeding behavior—vehicles exceeding 75 mph. Motorists driving between 66 and 75 mph are in violation of the posted speed limit but are not ticketed or detected by the SEP. The speed detection data were collected by the 6 enforcement cameras during the following warning, program, after, and reactivation periods:

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Warning period: 1/22/2006–2/21/2006 (31 days).
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Program period: 2/22/2006–10/23/2006 (244

Safety impacts

The assessments of safety impacts of the SEP are now presented. Preliminary analysis concepts are followed by a description of three analysis methods, their assumptions, and analysis results.

Conclusions and recommendations

The city of Scottsdale, Arizona demonstrated the first application of a fixed photo SEP in the US on a limited access urban interstate. This study analyzed the impact of the SEP on speeding behavior, traffic safety, and economic impacts of crashes. Three analysis approaches were used, including a before-after analysis with comparison site, a before-after analysis with correction for traffic flow, and an empirical Bayes’ analysis. All three methods produced similar results, with slight

Acknowledgements

The authors would like to thank all agency partners in Arizona for providing data, as in particular the city of Scottsdale and the Arizona Department of Transportation for funding and supporting the evaluation. The contents of this paper reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Arizona Department of Transportation, the Federal Highway

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Evaluation of the Scottsdale Loop 101 automated speed enforcement demonstration program☆

Abstract

Introduction

Section snippets

Literature review

Impact on ticketed speeding behavior

Safety impacts

Conclusions and recommendations

Acknowledgements

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Accid. Anal. Prev.

Time and distance halo effects of an overtly deployed mobile speed camera

The Handbook of Road Safety Measures

Safety impacts of differential speed limits for trucks and passenger cars on rural interstate highways: a modified empirical Bayes approach

J. Transport. Eng.

Econometric Analysis

The effects of automated speed enforcement systems on traffic flow characteristics and accidents in Korea

ITE J.

Observational Before-after Studies in Road Safety: Estimating the Effect of Highway and Traffic Engineering Measures on Road Safety