Driver behaviour, dilemma zone and safety effects at urban signalized intersections in Greece.

Driving behaviour at signalized intersections is one of the main factors contributing to the safety level of such entities. This behaviour, with respect to yellow signal obedience or violation, is examined at a signalized intersection in Thessaloniki, Greece. The data, collected for the study purposes, include vehicles' speeds and distance from stop line when exposed to yellow light, gender and age group of drivers as well as reaction of Platoon leaders and first followers. Drivers were grouped into three categories, namely conservative, normal and aggressive, according to their behaviour at the intersection, the existence of a dilemma or option zone and their initial approaching speed. A binary choice model was also developed relating the probability of stopping at the STOP line or crossing it as a function of approach speed, distance from intersection, gender, age group and the existence or not of a dilemma zone. The findings of this research indicate that a large percentage of drivers facing the yellow signal are caught in a dilemma zone due to high approaching speeds and exercise an aggressive behaviour. The distribution of drivers into the three categories changes with differing assumptions pertaining to the factors affecting the calculation of safe stopping distance and critical crossing distance as well as speed thresholds for determining a priori aggressive behaviour. The research concludes that aggressive drivers represent a high percentage of all drivers and measures towards improving driving behaviour and/or reducing vehicles' speeds are required.