Investigating road safety issues through a microsimulation model

Some papers have been recently presented (Cunto and Saccomanno, 2007; Cunto and Saccomanno, 2008; Saccomanno et al., 2008) on the potential of traffic microsimulation for the analysis of road safety. In particular, studies have confirmed that the reproduction by simulation of user behaviour under different flow and geometric conditions, can identify a potential incident hazard and allow to take appropriate countermeasures at specific points of the road network. The objective of this paper is to assess the validity of this approach and present a new methodology for investigating road safety issues. A calibrated microsimulation model has been developed to analyze vehicle trajectories, and hence vehicle interactions, in some different scenarios and verify traffic safety levels. The microscopic model allows the estimation of road safety performance through a series of indicators (Crash Potential Index, Deceleration Rate to Avoid Crash, Maximum Available Deceleration Rate, Time to Collision, etc.), representing interactions in real time between different pairs of vehicles belonging to the traffic stream. When these indicators take a certain critical value, a possible accident scenario is identified. The validation of the proposed methodology can be done by comparing the value assumed by safety performance indicators in simulated and real scenarios. The microscopic simulation model is also combined with a new video image traffic detection algorithm to detect vehicle trajectories. Microscopic traffic flow parameters obtained by video detection are, in fact, used to calibrate the microsimulation model. The above described methodology has been applied in the analysis of overtaking maneuvers on single lane for direction fast rural roads. Results indicate that the methodology can be useful in the estimation of safety performance indicators and in evaluating traffic control measures.