Meta-Analysis of Crash-Risk Factors in Freeway Entrance and Exit Areas

Entry and exit areas are considered critical parts of freeways and expressways. In order to meet traffic safety and operation requirements, it is important that ramps and speed-change lanes have the appropriate design so that vehicles may complete sequential maneuvers. However, literature on risks associated with these freeway elements is limited and has often demonstrated contradictory results. The present research meta-analyzes the effects of ramp and speed-change lane characteristics on crash outcomes. A random-effects meta-analysis was conducted on the effect of ramp length on crash severity, and a nonsignificant overall effect is observed. Similarly, random-effects meta-analyses regarding deceleration lane length suggested a nonsignificant effect on road safety (both on frequency and severity) at a 95% level of confidence. There is no indication of strong publication bias in any of the meta-analyses performed. Overall, the results suggest that, although several individual studies reported significant effects of these design elements on road safety, there is a need for further research, especially in a broader geographical context because of heterogeneous results. (C) 2017 American Society of Civil Engineers.