Effect of Heavy Transport Vehicles on Speed-Flow Characteristics of Mixed Traffic on Multi Lane Divided Intercity Highways

Many of the passengers and goods transportation operations are carried out by heavy transport vehicles (HTVs) like medium commercial vehicles (MCVs), heavy commercial vehicles (HCVs), and multi axle vehicles (MAVs) on multi-lane divided intercity highways. The presence of these HTVs in the traffic stream influences the overall characteristics of the traffic flow mix. The slow-speed movement of these vehicles in the median lane and kerb lane in the traffic stream affects the speed-flow characteristics of the mixed traffic, thereby deterring the speed of the other classes of vehicles, which eventually reduces the capacity of the traffic stream. The main aim of this study is to investigate and analyse the dynamic characteristics of HTVs occupying the high-speed lane (median lane) and low-speed lane (kerb lane). In order to gain a better understanding and qualitative overview of the HTVs' movement in the traffic stream, the data acquisition process was carried out using a transportable infra-red traffic logger (TIRTL) set up across one direction of the four-lane divided highway connecting the Chennai City with Nagapattinam City in India. Using the acquired data, dynamic passenger car units (DPCU) of each vehicle is estimated, and inferences are drawn concerning HTV's operating speed and flow. Also, a lane-based comparative study was carried out between the speed-flow characteristics of HTVs when these HTVs' are occupying the high-speed lane and low-speed lane during their operation on the multi-lane divided intercity highways. The analysis results showed that there is a significant drop in the capacity when the HTVs are operating on the high-speed lane at speeds lower than the desired operational speed when compared to that of the capacity when the HTVs are operating on the low-speed lane.