Evaluating the Effect of Heavy Vehicles on Traffic of Two-Way Two-Lane Road in Mountainous Area of Iran as a Developing Country

The presence of light and heavy vehicles will create a heterogeneous traffic flow. This heterogeneity exists in dimensions, speed, maneuverability, and performance. The difference in the performances of these two kinds of vehicle types will affect the traffic flow properties. For studying the effect of heavy vehicles (HV) on traffic flow properties, an undivided two-lane two-way road in Mazandaran, Iran, was selected as a testbed, and the changing in speed, lane changing number, travel time, and delay at different rates of HVs in both lanes were analyzed. The simulation in calibrated Aimsun software shows that increasing the heavy vehicles’ rate reduces the average speed of traffic flow up to 15% at 40% for HVs. The lane changing number will increase about 20% at the rate of 24% of HVs, and it will be around up to 40% when the rate is increased. Besides, the travel time of traffic flow increases by about 18% at the rate of 40% of HVs. Furthermore, the delay time increases up to 40% at the rate of 40% of HVs. Moreover, the effect of changing the opposite lane HVs ratio on traffic properties shows that the route’s traffic speed increases 12% due to increasing the HVs rate of 40% in the opposite lane. The users’ lane changing behavior shows no significant changes due to the increased HVs rate in the opposite lane. Travel time increases 12% at the rate of 50% of HVs on the opposite lane, and delay time decreases 20% due to the increasing rate of HVs in the opposite lane. The effect of increasing lane widening on the traffic flow properties was examined. The result shows that the average speed of traffic flow increases by about 27% by adding a new lane to the route. This change can assume to improve traffic properties. The lane changing number shows an increasing 100% after widening the lane, and it shows increases in driver’s maneuverability. Travel time decreases about 20% after added a lane, and vehicles’ delay time reduced about 30% after a new lane was added.