Effect of directional split and slow-moving vehicles on two lane capacity.

The 2000 Highway Capacity Manual (HCM) states that the capacity of a two-lane road is nearly independent of the directional split of traffic. However, a study conducted on two-lane roads in India has shown that capacity reduces as the split moves away from 50/50. The capacity of a two-lane road at even split in two directions is estimated as 2920 passenger car units per hour, which is less than the value specified in HCM 2000. The effect of slow-moving vehicles is also evaluated and it is found that capacity decreases as the proportion of slow-moving vehicles in the traffic stream increases. (a).