Effects of Traffic and geometric on hazardous manouver

The paper reports the outcomes of a large experimental study carried out using an advanced interactive driving simulator and aimed at analyzing the car-following behaviour and passing behaviour in different traffic conditions as well as different geometric configurations of the road alignment. A two-lane rural road more than 8 km long was designed and implemented in the driving simulator. The alignment had 15 different geometric elements: 8 tangents with length ranging between 200 m and 1000 m; 7 horizontal curves made up of approach clothoid, circular curve and departure clothoid. The radii of the circular curve ranged between 215 m and 1000 m. Four different traffic conditions in terms of traffic volume and speeds of opposing vehicles and impeding vehicles were simulated. Thirty-two drivers with ages ranging from 22 to 40, male (70%) and female (30%), drove in the simulator on the four scenarios. The differences in speed and position between the driver’s vehicle and the other vehicles on the road were collected in order to: a) identify the hazardous carfollowing and passing manoeuvres; b) calculate the parameters proposed in literature for the evaluation of the rear-end and head-on collision risk; c) evaluate the effects of traffic on driver behaviour during the two manoeuvres; d) analyze the influence of the geometric features of the road on the risk associated with car-following manoeuvre. As regards the car following manoeuvres the measures of risk chosen in this study were the most advanced Time-to-Collision-based parameters: Time Exposed Time-to-collision (TET) and Time Integrated Time-to-collision (TIT). As regards the passing manoeuvres the evaluation of risk was entrusted to the remaining gap to the oncoming vehicle at the end of the passing manoeuvre. The results of the correlation analysis between the rear-end risk parameters and traffic and geometric features suggest that the traffic conditions affect mainly the car-following behaviour. Also the geometric elements of the alignments have a significant role. Particularly the influence of the geometric features tends to stop when the traffic intensity reaches high levels. In these conditions the driver’s behaviour is affected exclusively by vehicle interferences. Concerning the passing behaviour the outcomes of the analysis show that the accepted risk by driver increases as the traffic intensity increases. High traffic intensity leads the driver to carry out hazardous passing manoeuvres.