Operating speeds from driving simulator tests for road safety evaluation

Two-lane rural roads with features consistent with those required by Italian guidelines for major two-lane rural roads were implemented in a driving simulator. Twenty-nine tangent-curve-tangent configurations similar to those where a previous validation study ascertained the validity of the driving simulator for driving speed behavior research were selected. The drivers’ speeds on these configurations were processed to obtain the operating speeds. The main findings were the following. The maximum operating speed on the last 200 m of the approach tangent (V85max 200) is higher than the operating speed at the midpoint of the tangent (V85mid,t). The operating speed at the midpoint of the curve (V85mid,c) overestimates the minimum operating speed of the drivers on the curved section (V85min,c). Therefore, V85max 200 and V85min,c are the most appropriate parameters for the quantification of the speed differential as difference between the operating speeds on the approach tangent and on the successive curve. A positive correlation was found between V85max 200 and the length of the tangent whereas a negative correlation was found for the longitudinal grade. Two operating speed models for curves were obtained. Such models were validated using the speeds that were recorded by means of a Global Positioning System device on six configurations of a real two-lane rural road.