Example Analysis and Handling of Uncertainty in the Highway Capacity Manual with Consideration of Traffic Diversion

Dealing with uncertainty is inevitable when the performance of transportation systems is estimated and predicted. Various sources of uncertainty and how uncertainty can be handled are demonstrated. An example single stream at an unsignalized intersection is considered as an illustration. The data collected in the field were used to present sources of uncertainty and their contribution to prediction error. Interval values are proposed to represent the prediction uncertainty. This approach is advantageous over rigorous statistical estimation when distributions of the variables and interactions between them are not well specified. Also addressed is drivers’ adjusting behavior to changing traffic performance. A simple volume elasticity approach is used to address traffic diversion and to provide realistic estimation of interval values of future delay. This study should be a useful introduction to the uncertainty issue in traffic analysis based on the Highway Capacity Manual.