Safety Evaluation of Left-Turn-Lane Line Width at Intersections with Opposing Left Turn Lanes

摘要

The objective of this research project was to evaluate the effectiveness of offset opposing left-turn lanes at signalized intersections in reducing the frequency and severity of left-turn related accidents. The Cities of Lincoln and Omaha offset opposing left-turns by widening leftturn lane lines in June 1999 at six intersections. The research team investigated traffic accident patterns between January 1994 and December 2002 at those six intersections by making comparisons with two control intersections (i.e. intersections at which left-turns were not offset by lane line widening) using a four-step research methodology. First, existing literature was reviewed to determine the extent and availability of materials relevant to this project. Second, accident data were collected for the six study and two control intersections. The third step involved the analysis of the collected data. Four analysis techniques were employed to assess the effectiveness of off-setting opposing left- turn lanes by using wider left-turn lanes lines. Results from the trend analysis of accident frequencies and accident rates presented a mixed picture of the 'before' (pre-June 1999) and 'after' (post-June 1999) data. In the absence of a clear-cut increasing or decreasing trend in the accident frequencies and rates, the research team conducted an in-depth analysis of the collected data. Accidentlcrash rates were analyzed by using linear regression while accident frequencies were re-analyzed by the Before-After (B-A) analysis and by using Poisson regression modeling. Crash rate modeling showed mixed results since rates were increasing and decreasing at various intersections with time and either increased or decreased in the 'after' time period. Only the 72nd and Cass intersection in Omaha appeared to have experienced statistically significant crash rate reduction.