An Assessment of Interstate Safety Investment Priorities in Washington State Morgan State University The Pennsylvania State University University of Maryland University of Virginia Virginia Polytechnic Institute & State University West Virginia University The Pennsylvania State University The Thomas D. Larson Pennsylvania Transportation Institute Transportation Research Building University Park, PA 16802-4710 Phone: 814-865-1891 Fax: 814-863-3707 www.mautc.psu.edu Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. 4. Title and Subtitle 5. Report Date Assessment of Interstate Safety Investment Priorities in Washington State December 1, 2014 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Venky Shankar, Minho Park, Junseok Oh, Sudhakar Sathyanarayanan, and LTI 2015-11 Vikas Sharma MAUTC Report No. PSU-2011-02/ PSU-2012-03 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) The Thomas D. Larson Pennsylvania Transportation Institute The Pennsylvania State University 11. Contract or Grant No. 201 Transportation Research Building DTRT-07-6-0003 University Park, PA 16802 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered The Pennsylvania Department of Transportation Final Report 11/7/2011 – 12/31/2012 Bureau of Planning and Research Commonwealth Keystone Building 400 North Street, 6th Floor 14. Sponsoring Agency Code Harrisburg, PA 17120-0064 15. Supplementary Notes 16. Abstract The Washington State Department of Transportation (WSDOT) commissioned the current study, targeting the entire interstate mainline network in Washington State, to provide strategic direction to multi-biennial investment interstate locations that offer the greatest return in terms of cumulative and annualized safety benefits. The objectives of this study were to prioritize interstate locations strategically in terms of risk of high social cost, while targeting locations that repeat in nature. As such, the methodological questions that arise relate to the following: what measurements are required to comprehensively address the “strategic risk evaluation” aspect, and what measurements are required to adequately address the “repeat location identification” aspect. Using a step-wise procedure to systematically assess mainline interstate accident risk, a multi-objective approach was employed in order to factor in multiple criteria for ranking of segments, while accounting for multiple accident types as inputs in the ranking process. The planned scope of this study produced a target priority list of 202 locations with a total length of 154.5 miles. This list should be evaluated in detail for scoping improvements, associated costs and benefits prior to evaluating locations in the “tracking list.” The next step in ensuring implementation and successful deployment of this procedure will be to carefully evaluate cost improvement strategies and estimate associated benefits. Once costs and benefits are computed, one can systematically proceed to evaluate various measures of cost efficiency and effectiveness using lifecycle and annualized benefits and costs. 17. Key Words 18. Distribution Statement Interstate mainline network, accident risk, investment, safety benefits, No restrictions. This document is available strategic risk evaluation, repeat location identification from the National Technical Information Service, Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 18 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. This document is disseminated under the sponsorship of the U.S. Department of Transportation’s University Transportation Centers Program, in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof. AN ASSESSMENT OF INTERSTATE SAFETY INVESTMENT PRIORITIES IN WASHINGTON STATE REPORT PREPARED BY Dr. Venky Shankar, PE Principal Investigator and Associate Professor The Thomas D. Larson Pennsylvania Transportation Institute Department of Civil and Environmental Engineering 226C Sackett Building The Pennsylvania State University University Park, PA 16802 Tel: (814) 865-9434 E-mail: [email protected] Minho Park Doctoral Candidate in Civil Engineering Department of Civil and Environmental Engineering The Pennsylvania State University Junseok Oh Doctoral Candidate in Civil Engineering Department of Civil and Environmental Engineering The Pennsylvania State University Sudhakar Sathyanarayanan Transportation Engineer DKS Associates, Inc. Seattle, WA 98104 And Vikas Sharma Transportation Engineer Olsson Associates, Inc. Phoenix, AZ 85020 TABLE OF CONTENTS INTRODUCTION ...........................................................................................................................1 GOALS AND OBJECTIVES ..........................................................................................................3 SCOPE OF THE STUDY ................................................................................................................4 STUDY METHODOLOGY ............................................................................................................7 Safety priority evaluation process step one: screening and segmenting the network .................8 Safety priority evaluation process step two: defining accident-based prioritization criteria ......9 Safety priority evaluation process step three: computing segment-specific inputs ...................10 Safety priority evaluation process step four: prioritizing and estimating accident reduction targets ...................................................................................................................11 Safety priority evaluation process step five: determining improvement strategies ..................13 CONCLUSIONS AND RECOMMENDATIONS ........................................................................14 REFERENCES ..............................................................................................................................17 LIST OF FIGURES Figure 1 Accident Distribution Across the Seven Interstates in Washington State in 2002-2006 ...................................................................................................................7 Figure 2 Process Flowchart .....................................................................................................15 iii Introduction The Washington State Department of Transportation (WSDOT) embarked on a statewide traffic safety initiative in the early 1990s to enable the systematic assessment and treatment of accident risk on state highways. The initial effort was targeted at roadway segments on a sample of the entire state highway system for which risk models were developed and tested (Milton and Mannering 1998). The models were statistical in nature and provided a framework for estimates of overall accident risk. The structure of the models was similar to that employed in early accident modeling work by Shankar et al. (1995) in the analysis of safety risk on Interstate 90 near Snoqualmie Pass. In the 1995 study, Shankar laid out the foundation for modeling both frequency- and severity-oriented risks. The 1998 models from the Milton study applied the frequency framework to segment accident risk. These models were supplemented with a roadside accident risk framework that enabled the estimation of run-off-the-road accidents. Around 1997, about five years since the inception of the statewide safety assessment initiative, a targeted effort involving the refinement of statistical models for roadway segments was conducted (Shankar et al. 1997). Complementing this advanced effort was an attempt undertaken by the WSDOT Design Policy and Standards branch to quantify the risk of median crossovers on state highways (Shankar et al. 1998; Albin et al. 2001; Glad et al. 2002; Chayanan et al. 2004). At the turn of the century, efforts continued in the area of severity modeling, which WSDOT viewed as an important step in the development of a systematic process. Initial testing of severity-oriented models was based on early work by Shankar et al. (1996) that analyzed severity risk under inclement conditions on Interstate 90 near Snoqualmie Pass. Other studies conducted by WSDOT safety researchers targeted non- motorized modes such as pedestrian travel. In a study published in 2003, Shankar et al. provided a statistical framework for the analysis of mid-block pedestrian accident risk, and complemented this effort by examining the risk of pedestrian severity in a subsequent study published in 2006. Milton et al. 1 (2008) concurrently applied a state-of-the-art statistical framework to assess the risk of frequency and severity simultaneously. In a paper published in 2008, Milton et al. laid out the foundation for the analysis of segment and intersection accident severity proportions. This study was meant to provide a methodological completeness to the study of high accident locations and corridors (HAL, HAC) and pedestrian accident locations (PAL), long established in WSDOT practice as the three basic modalities of network safety analysis. The above-described studies provided utility in the forecasting of accident risk – they employed historical data related to accident