Objective: The safety benefit of stop sign treatment employed at passive highway-rail crossings has been a subject of research for many years. The objectives of this research is to investigate whether and to what degree the crash rate has changed at previously passive grade crossings after stop signs were implemented and examine whether and how the crash characteristics (associated with vehicle type, crossing surrounding, crossing design, crash severity, etc.) changed subsequently.
Methods: Federal Railroad Administration grade crossing databases during the 26-year period (1980-2005) were applied in this study. Among the stop-controlled grade crossings, a total of 7394 "target" crossings were identified to be once crossbucks controlled and subsequently upgraded with the installation of stop signs without the implementation of other traffic control devices during the study period. Each target crossing was further divided into two time periods: when it was controlled by crossbucks only (before) and when it was controlled by stop signs (after). Both annual crash rate analysis and crash propensity analysis of before-after stop sign installation are conducted to quantify the safety benefit of stop sign treatment.
Results: It was found that during the 26-year period (1980-2005), the annual crash rates when the crossings were controlled by crossbucks-only were consistently higher than the crash rates when the crossings were controlled by stop signs. The further crash propensity analysis indicated that the stop sign treatment was especially effective at crossings with higher annual average daily traffic (AADT), advanced warning signs, sight distance problem, adverse lighting conditions; the motorist-stopped-on-crossing, did-not-stop, and injury crash risks were also significantly reduced after stop signs were applied.
Conclusions: The finding of this study suggested that the vehicle volume should be included into the guideline for stop sign use. Therefore, engineers and decision makers are encouraged to routinely check available sight distances at passive crossings controlled by crossbucks only and add stop signs to the crossings with insufficient sight distances. Additionally, it is suggested that advanced warning signs should be jointly used at stop-controlled crossings to maximize the safety effect. However, stop signs were less effective at crossings with higher train speeds or track classifications, where active warning devices may be a better safety solution for grade crossings.