An evaluation of freeway capacity in Texas

The current value of freeway capacity and the speed flow relationship have been questioned as a result of observations of flow rates much higher than 2,000 passenger cars per hour per lane (pcphpl) and the recent revision of the multi-lane highway chapter in the Highway Capacity Manual. An analysis of freeway capacity in Texas found greater variability in free-flow flow rates and determined that queue discharge is the best estimate of maximum sustainable flow. Queue discharge flow rates averaged 2,225 pcphpl but were measured as high as 2,400 pcphpl for individual lanes. Based on the analysis, a speed-flow model was developed and the maximum sustainable flow rate was determined to be 2,200 pcphpl, which is the value recommended for freeway capacity in Texas.