Investigating Car-Following Behaviour on Italian Highway

"\"Time Headway (TH) and Time To Collision (TTC) are indicators used to estimate the safety of traffic situations. Specifically such indicators are related to the likelihood of rear-end collisions during car-following driving situations.. In this study TH and TTC were computed and compared on the basis of data recorded by means of a system of traffic control on an Italian highway. Four measurements sites and two days of investigation allowed collecting a wide database of almost 200000 vehicles, whose about the 50% were travelling in car-following situations.. The main objectives of the paper consisted in:. \\tverifying that, on highways, the two indicators, TH and TTC, are independent of each other and therefore do not provide the same information on the driver behaviour in car-following situation but could be used for evaluating different conditions;. \\tanalyzing the extent to which TH and TTC are conditioned by the different visibility conditions (day or night driving), the type of lead vehicle (passenger car or heavy vehicle) and the type of travelling lane (left or right).. Results showed that TH and TTC can be considered as practically independent of each other, providing different information about driver behaviour in car-following situations. Moreover it was found that shorter THs are used by the following driver during daytime, behind passenger vehicle and driving on the passing lane. On the contrary only few cases with critical TTC values were recorded, demonstrating that TTC is more effective for detecting impending dangerous situations.. \""