ABSTRACT
The concept of design consistency refers to the conformance of road geometry with driver expectancy. An inconsistency in road design can be described as a geometric feature or a combination of features with unusual or extreme characteristics that may lead to unsafe driving behavior. A handful of methods and approaches have been trying to model design consistency. One of the most used criteria to evaluate design consistency is based on operating speed measurement. The present Portuguese design manual proposes a method to evaluate the geometric design consistency that is usually considered too simplistic, assuming that the speed on the curve is uniform and the values of the acceleration and deceleration are based on constant values. To investigate the limitations of this approach, field measurements were recorded using a vehicle equipped with a precision data logger that combines video footage with kinematic variables. The analysis of the resulting database has shown that some assumptions of traditional speed models do not hold and has motivated the development and calibration of a speed model on curves for two-lane rural highways. This model can differentiate the driving dynamics of a set of drivers on two-lane rural highways under a wide range of geometric conditions and can be integrated in a global methodology to assess design consistency on two-lane rural highways.
