Vissim-based Simulation of Variable Slip Road Length Design of the Federal Highway in Malaysia

Abstract

Traffic congestion on highways is mainly the result of overcrowding. This phenomenon happens when a great number of vehicles storm the road, disrupting the smooth flow of traffic. In this study, traffic simulation, using PTV Vissim software as a scenario planning tool, was conducted to analyze slip road length as a traffic congestion source at a selected intersection point. The intersection point was designed based on Federal Highway between KM14.8 and KM14.5 in Shah Alam. The VISSIM model was calibrated using traffic flow, delay time, average number of vehicles and maximum queue length data obtained from one-hour instances of video recordings of the respective intersection during evening peak periods. Based on the field data, the average throughput is 1003 vehicles with an average speed of 40 m/s. The traffic condition in the area can be regarded as congested. One of the reasons for congestion in this area is the proximity between in and out feed to the Federal Highway. Three different distances between in and out feed to the Federal Highway were simulated, which were 140m, 280m (baseline) and 420m. Based on the results obtained from the simulation, it could be gathered that the longer the slip road, the higher the length of delay. However, the distance of the in/out feed had little to no effect in terms of vehicle throughput. While running the simulation, it could be observed that the delay mainly occurred due to merging and lane-changing activities at the input. Nonetheless, further analysis is needed for different slip road settings to conclude congestion pattern based on road design.