Estimated passenger car equivalent using backward wave speed

In previous studies, little attention has been paid to developing methods for estimating passenger car equivalent (PCE) factors under oversaturated conditions. This paper presents a new method to estimate PCE factors for heavy vehicles based on the assumption that backward wave velocities keep consistent under oversaturated conditions. As the variations of backward wave velocities in mixed flows will be minimal if the traffic stream is uniform, a minimum relative standard deviation optimising model is given based on backward wave velocity. The traffic data drawn from I-80 datasets provided by the next generation simulation are utilised to analyse this method and prove the assumption. In view of the limitation of empirical data, Vissim microscopic traffic software is used to simulate oversaturated traffic flow under different percentages of heavy vehicles. The results show that the effects of heavy vehicles under oversaturated conditions are greater than those under free-flow conditions and the proportion of heavy vehicles has a major impact on the PCE factors.