In-Service Performance Evaluation (ISPE) of Median Cable Barriers and Strong-Post W-Beam Guardrails on Interstate 85 in Alabama

摘要

This study presents an in-service performance evaluation (ISPE) of high-tension median cable barriers and strong-post W-beam guardrails along Interstate 85 (I-85) in the State of Alabama. Crash data from 2012 to 2016 were used. The study compares the safety performance of median cable barriers and median guardrails in terms of crossover/non-crossover percentages and injury crash percentages. The study also conducts an ISPE of roadside guardrails on I-85. Extensive data collection effort has been made through reviewing in detail police reports and capturing features rarely explored in previous studies, e.g., median width, left shoulder width, barrier offset distance or lateral position (i.e., distance from barrier to median edge), blockout type, and number of cables/strands. A total of 495 crashes were used, broken down as 220 median cable barrier crashes (MCBCs), 79 median guardrail crashes (MGCs), and 196 roadside guardrail crashes (RGCs). Roadside guardrails showed the highest success in preventing crossover crashes (98%), followed by median cable barriers (94.5%), and finally median guardrails (86.1%). Median cable barriers were more successful in preventing sport utility vehicle (SUV) crossovers (91.2% success rate) compared to median guardrails (79.2% success rate). Median cable barriers had less injury crash involvement (12.7%) compared to median W-beam guardrails (34.2%). It was also found that composite blockouts were more involved in injury-related median guardrail crashes (32.9%), as opposed to roadside guardrail crashes (23.3%). Some recommendations from the study have included ensuring installing cable barriers on medians that are at least 50-ft wide, as well as ensuring installing W-beam guardrails on medians that are 50-70-ft wide.