Evaluation of models for estimating free-flow speed on two-lane rural highways in Brazil

The objective of this article was to evaluate different models found in the literature to estimate the free-flow speed (FFS) on Brazilian two-lane rural highways. The models available in three editions of the Highway Capacity Manual (HCM) and two adaptations of the manual were evaluated to reproduce the behavior found on Brazilian highways. This evaluation was carried out based on traffic data collected in nine homogeneous segments of a Brazilian highway (MG-050) in the state of Minas Gerais. The FFS results estimated with the analytical methods were compared with the FFS data observed directly in the field. It was identified that there is no correlation between the FFS values produced by the analytical methods and the values found in the field. However, two models, one HCM2000 and another HCM2022, adapted to Brazilian traffic conditions, have similar average FFS values to those observed in the field.