Speed models and criteria for assessing traffic performance on two-lane highways

In the widely used HCM and HBS assessment methods of the traffic performance of two-lane highways speed models are an essential element of the analytical methodology. Differences in the approach to analyses, as well as differing numbers of determinants taken into account and criteria used to assess traffic performance may all produce disparate results and reduce the practicality of the application of these methods. The paper compares the HCM and HBS speed models and demonstrates key differences in their approach to the impact of traffic volume, the share of heavy vehicles and longitudinal gradients of the road. The assessment of traffic performance by both methods also demonstrates significant differences in assessments, especially in more adverse road and traffic conditions. The paper will also show assumptions underlying the choice of research sites, methods of traffic research, databases and selected results of analyses as well as the impact of selected factors on speed and speed regression models