Offsetting Opposing Left-Turn Lanes at Signalized Intersections: A Safety Assessment Case Study in Lincoln, Nebraska

Opposing left-turning vehicles at signalized intersections block each others’ view of oncoming traffic. The ability to see oncoming traffic is critical for safe negotiation of left-turns at intersections during a permitted left-turn phase of the signal. Offsetting of opposing left-turn lanes at signalized intersections improves sight distance for left-turning motorists. This paper reports on a case study conducted in the City of Lincoln, Nebraska that was aimed at analyzing the safety benefits from offsetting opposing left-turn lanes at signalized intersections. Data from before-after scenarios were analyzed using the empirical Bayes procedure, which accounts for the effects of regression to the mean. The multivariate regression method was used to estimate the expected number of crashes for a reference population of 36 non-treated intersection approaches with similar geometric and traffic characteristics as the treated sites. These estimates were then used to determine the expected number of crashes at the treated sites in the ‘after’ period, had the treatment not been applied. Results from this study indicate a 1.5 percent change in safety. Based on the results, the author concludes that safety improved (but only minimally) at the three treated intersections as a result of offsetting opposing left-turn lanes.