Microscopic Analysis of Climbing Lane Performance at Freeway Uphill Section

Abstract

Freeways which are designed for high-speed vehicular traffic seems to have some problems with the sections with inclines due to the performance drop in accelerations of heavy trucks and high occupancy vehicles (HOVs). To complement this problem, installing auxiliary lane to laterally separate low speed vehicles from high speed vehicles. This is called a climbing lane. There are mainly two types of climbing lane: 1) pocket type climbing lane and 2) overtaking type climbing lane. In Korea, many sections with inclines are located near urban area, leading to some attentions on the performances of climbing lane at various traffic input flow conditions. To do so, microscopic traffic simulator based on OFFA is used for analysis. Some adjustments are made on the OFFA to depict asymmetric behavior without short gap mode and to demonstrate performance drop of heavy truck vehicles. Total delay is used to evaluate operational efficiency and time to collision is used to evaluate safety performance. As a result of simulation study, the overtaking type usually showed better performance in both operational efficiency and safety performance. However, at some traffic input flow with high truck ratio conditions, the performances of overtaking type climbing lane broke down, showing low operational efficiency and safety performance. Therefore, climbing lane operation depending on the traffic demand should be considered.