Estimating traffic performance on Spanish two-lane highways. Case study validation

Spanish standards rely on the procedures of the U.S. Highway Capacity Manual (HCM) in order to analyze traffic efficiency. Given the differences in road environment, driving behavior and vehicles’ performance, the HCM procedure would not be completely suitable for application to Spanish conditions. Moreover, the effect of passing restrictions is considered through the percentage of no-passing zones and significant variations on the horizontal alignment are not included on the uniform segment identification; which can lead to unrealistic results. The objective of this paper is to twofold: (1) modify the HCM two-lane highway analysis procedure for Spanish conditions considering the effect of passing restrictions and highway alignment variations on two-lane highway operation; (2) compare on one case study the results from the proposed approach and the HCM analysis procedure. The results indicate that solely geometry was not enough to characterize traffic operation on the straighter alignments (almost tangent), where speed dispersion was up to 20 km/h, and passing restrictions should be also included. Moreover, PTSF varied significantly depending on average passing zone lengths. The case study indicated that the proposed methodology provides more accurate estimates than the HCM on actual (in operation) two-lane highways. The proposed approach combines the effect on highway performance of passing restrictions, as considered on the US HCM, and highway alignment, as considered directly on the German HCM. The impact of trucks is modeled through the percentage of trucks rather than PCEs values, as it is common practice in Spain and Germany. This approach is simpler and more flexible to model the impact of trucks, passing restrictions and highway alignment on the different performance measures.     «

Spanish standards rely on the procedures of the U.S. Highway Capacity Manual (HCM) in order to analyze traffic efficiency. Given the differences in road environment, driving behavior and vehicles’ performance, the HCM procedure would not be completely suitable for application to Spanish conditions. Moreover, the effect of passing restrictions is considered through the percentage of no-passing zones and significant variations on the horizontal alignment are not included on the uniform segment ide...     »