Cumulative lateral position: a new measure for driver performance in curves

Vehicle control can be described with lateral and longitudinal control measures. The Standard Deviation of Lateral Position (SDLP) is probably the most common measure to reflect lateral control. Indices such as mean Lateral Position (MLP) and Time-to-Line Crossing (TLC) have also been used to describe driver behaviour. Even though all these measures have demonstrated their value, in some specific cases, these measures may indicate that driver behaviour is deteriorated while that may not necessarily be the case. When negotiating curves for example, most drivers prefer to not to follow the centre of the lane. We propose a new index, called the Cumulative Lateral Position (CLP), an index that does not suffer from drawbacks of the earlier mentioned measures in these conditions. We also applied the CLP in a practical case. In a simulator experiment drivers negotiated three types of curves: traditional circular (CIR), clothoid (CLO), and a new curve, a polynomial curve with continuous curvature (CON). Results show that the CLP index, unlike the older measures, is able to well summarise the trajectory on a road curve and is sensitive in distinguishing different driving behaviour with respect to variations in road geometry, even in cases where these differences are small. The proposed methodology can be used to evaluate both new and existing roads design solutions, and showed in this experiment that driving behaviour was safest in the continuous curve.