Institute of Transportation, MOTC

      There is no clear left-turn design specification for intersections in Taiwan, so that local governments have no solution to improve road design at intersections which occurred left-turn vehicle crashes frequently; Besides, the design of left-turn lanes vary greatly in different places. Therefore, the purpose of this study is to evaluate the safety effectiveness of different types of left-turn lanes, and considered the similar type of left-turn lanes, the safety effectiveness of left-turn lane elements. To consider the effect of the complexity of crash types, past literatures mostly discuss the specific crash types during different crash types or crash severity. However, this will result in 2 problems, which is low-sample mean of specific crash pattern and high correlation among multiple crash patterns. The problems above may cause the coefficient estimate biase. Therefore, this study uses Multivariate Poisson Log-Normal model to solve the above problems.
       This study collects 61 intersection approaches for a total of 5 years in Taipei as sample, where Y considered as the crashes related to left-turn lane design (including same direction crash, rear-end crash, and left-turn side crash) and the types of vehicles involved in crashes (including motorcycle-motorcycle crash, motorcycle-car crash, and car-car crash). Compared to non-offset taper design, the number of crashes in full-offset taper design would decrease 44.1% same direction crashes, 55.9% rear-end crashes, 38.1% left-turn angle crashes, 38.9% motorcycle-motorcycle crash, 55.8% motorcycle-car crash, and 36.5% car-car crash. In summary, in order to reduce the crashes at intersection, the full-offset taper design is recommended as the prior choice in left-turn lane design, and the left-turn lane design elements should be considered in specific range.