Estimation of Design Lengths of Left-Turn Lanes

This study is to evaluate the simulation-based and analytical-based methods for determining the left-turn lane queue storage length and deceleration length. Four traffic models were selected to estimate left-turn queue length, including analytical-based models [i.e., Highway Capacity Software (HCS+) and Synchro] and simulation-based models (i.e., SimTraffic and VISSIM). Recommendations were given on the basis of the accuracy levels and the costs of these models in terms of time. A simulation-based method for determining the required deceleration length was developed by using VISSIM. The results from this method were compared with different agencies’ guidelines, which were developed by analytical-based methods. A procedure is recommended in this paper for estimating the total left-turn length on the basis of the estimated queue storage length and the deceleration length.