System-wide Safety Analysis of a Complex Transportation Facility: Urban Freeway Off-ramps

Highway safety has been a priority for many years now. A system-wide crash analysis is a practical solution when only a limited budget is available for improving safety of highways. A systematic approach, in contrast to a hotspot analysis, allows for a widespread installation of lower-cost countermeasures across the highway network. This study focuses on the safety evaluation of a particular facility type, urban freeway off-ramps, in terms of its geometric and traffic characteristics. 144 off-ramp segments in Richmond, VA were evaluated based on the crash data available from 2011 to 2015. A statistical model was developed that relates crashes to the geometric and traffic characteristics of each off-ramp segment. A test for independence was performed to identify if a statistically significant difference existed between type of collision and severity of crashes with respect to ramp geometry and traffic control. Significant geometric and traffic variables were then identified from the model and independence test to assist in the selection of low-cost countermeasures. AADTs of both freeways and off-ramps were found to be the most statistically significant variables. Installation of advance warning signs for better traffic management near the freeway diverge area and clearing roadsides of fixed objects to reduce rear-end collisions are low-cost solutions for crashes on urban off-ramps in the study area. The results of this study demonstrate an approach to safety evaluations that could support transportation planners and agencies in identifying system-wide locations to install or apply appropriate low-cost countermeasures. System-wide Safety Analysis of a Complex Transportation Facility: Urban Freeway Off-ramps Shalini Sankaranarayanan General Audience Abstract Efforts to improve highway safety has been a priority for many years now. An approach that considers all the locations in the network as opposed to considering only high crash locations helps in identifying low-cost countermeasures that can be installed across the highway network. This study focusses on the safety evaluation of urban freeway off-ramps. 144 off-ramp segments in Richmond, VA were evaluated based on the crashes that occurred on them from 2011 to 2015. The results from the safety evaluation identified geometric and traffic characteristics that led to a crash on the off-ramp segments. It was also determined whether type of collision and severity of crashes varied with geometry and traffic control. The results from the study assisted in selecting low-cost countermeasures that can be implemented across the highway network. Traffic volume of both freeways and off-ramps were found to be a significant cause for crashes. Installation of advance warning signs where off-ramp segments leave the freeways and clearing roadsides of fixed objects are some of the low-cost solutions to reduce off-ramp crashes. This study demonstrated an approach to safety evaluation that could help transportation planners and agencies in identifying locations across the highway network to install or apply low-cost countermeasures.