European Speed Environment Model for Highway Design-Consistency

The European road network is very large, and much of it is made up of two-lane rural roads. In Italy the road network requires adjustment work to improve mobility safety management. One of the most important tools for this analysis is the operating speed (V85) profile. In many design standards, different formulations are used for estimating V85, obtained on the basis of research carried out at different times and in different contexts. The aim of the research presented in this study is to analyze driver speed behavior on two-lane rural highways. The study was conducted using traffic counters, able to record in both directions and for every passage of a vehicle, its length, instant speed and direction. The survey plan was elaborated to satisfy different research objectives. The readings were taken by keeping every section under observation for 3, 6 or 12 hours. The data were collected on 11 homogeneous sections of highway. The database consisted of free-flow passenger car speeds and various geometric data from 103 sites. Data were collected at sites to both develop and validate equations. The proposed model includes the radius of horizontal curvature and the “Speed Environment†, which is defined as the speed at which users travel in free-flow conditions when they are not constrained by the alignment of the highway.