Modeling detection of incidents by drivers

An analytical model was developed to assess the detection of freeway incidents by drivers using advanced communications technologies. Drivers can report incidents to a highway agency by voice or by digital messaging either directly or through roadside beacons using a fixed or portable wireless communications system such as a cellular telephone. A FRESIM model was used to simulate shoulder and lane-blocking incidents occurring under variable traffic flow rates. The proportion of drivers with an in-vehicle communication medium arriving upstream of an incident and the degree of the drivers' reporting propensity were introduced as controlled variables. A discrete probability model was used to represent binary reporting decisions of drivers arriving upstream of an incident. The results showed that all incident types that were simulated could be detected in a short time with high probability of detection. The data indicated that all incident types, regardless of the prevailing traffic volume at the time of their occurrence, were detectable in less than one minute if one of five drivers on a freeway had an in-vehicle communication medium and was willing to use it to report the incident. Of special importance is that at the end of 1995 there was one cellular telephone user per five licensed drivers in the United States. The results of the modeling further showed that other factors affecting the detection performance of a driver-initiated incident detection process were the willingness of drivers to report incidents, the length of roadway within which an incident is visible to a driver, and the austerity of the highway agency's procedure for mitigating false reporting.