Abstract: Level of Service (LOS) is the measure recommended by the Highway Capacity Manual to evaluate roadway facilities’ operational condition. It is generally agreed that for signalized intersections, LOS is related to traffic safety. However; this relationship is not well established because operational condition and safety are rarely considered concurrently. In this study, LOS and crash data were acquired over a 3-year period from 164 four-legged signalized intersections in the Central Florida area. The LOS-safety relationship at the intersection approach level was investigated for different crash types using Bayesian inference. LOS was calculated for morning peak, midday, and afternoon peak. Because crashes occurring on different approaches within one intersection are likely to be affected by some unobserved variables’ influence, Random Effects Negative Binomial models were used. Results showed signalized intersection approaches operating at level LOS C (LOS A is highest, F is lowest) were associated with fewer total and rear-end crashes compared to LOS D, E, and F, and approaches operating at LOS A and B were associated with fewer total and rear-end crashes than LOS C. Left turn crashes were not associated with LOS. Time varying effects of LOS on crash occurrence were examined using Random Parameter Negative Binomial models. The results showed the effects of a specific LOS on total or rear-end crashes varied across different time periods, but the variation trends were not consistent for different LOS. This study shows an understanding of LOS-safety relationship at the intersection approach level requires examining different crash types and time periods.
Xuesong Wang, Jia Li, Rongjie Yu, Paul Tremont. Relationship between Level of Service and Traffic Safety at Signalized Intersections, Transportation Research Board 95th Annual Meeting, Washington D.C., USA, 2016. 1.10-14.