Evaluation of the 2010 Highway Capacity Manual Urban Street Free Flow Speed Prediction Model

摘要

The performance of the new 2010 Highway Capacity Manual (HCM 2010) procedure which predicts free flow speed using posted speed limit and eight additional variables was evaluated. The eight additional variables are the proportion of segment length with restrictive median, the proportion of segment with curb on the right-hand side, the number of access point approaches on the right side in the subject direction of travel, the number of access point approaches on the right side in the opposing direction of travel, the segment length, the width of the signalized intersection, the number of through lanes, and the distance between intersections. Multi-day speed data from 104 Florida urban street segments with speed limit ranging from 25 MPH to 55 MPH were used in the study. Field mean free flow speed was determined for each analysis segment as well as the above geometric and traffic attributes required by HCM 2010 to predict free flow speed. Statistical and graphical analysis of the HCM 2010 speed predictionmethodology showed that it had a low coefficient of determination (R~2) and that it under predicted free flow speed when segment posted speed limit was 35 mph or higher. The results further showed that the use of free flow speed (predicted by the HCM 2010 methodology) in determining arterial level of service produced lower levels of service for 10 of the 20 segments analyzed. In addition, calibration of the HCM 2010 model coefficients showed that speed prediction by this model can be improved if the speed limit coefficient is doubled and the influence of cross section and access density factors substantially decreased.