|Within many metropolitan areas, existing TMCs utilize operators and on-roadway equipment such as Closed Circuit Television Cameras (CCTV) to detect, verify, send response to, and close incidents. These functions however are typically only performed for incidents on freeways. In many areas, data from other roadways are simply not available. In addition, some TMCs do not collect data for all incidents visible to their operators, but only for those incidents that block lanes. Due to the inconsistencies in available data across regions, it is important that any reported TIM performance measures be properly defined and put into context, such as incidents occurring on freeways or on roadways with TMC coverage. This is especially important when reporting TIM performance metrics to a higher level, such as the region, state, or nationally, to ensure that “apples-to-apples” comparisons are being made.
An example of how incident data are gathered by a TMC comes from the Freeway and Arterial System of Transportation (FAST) in Las Vegas, Nevada. The figure above shows the incident input screen from the FAST system. It can be seen that the TMC operator must identify a variety of information about an incident, including the incident start time, incident type, number of lanes blocked, which lanes are blocked, incident severity, the time a tow truck arrived, the time the lanes were cleared, whether a truck was involved, and whether the incident is a secondary crash, among others. This particular TMC incident entry screen illustrates that FAST operators can record the data elements necessary to calculate roadway clearance time and secondary crashes (two of the three national performance measures), as well as multiple data elements for putting the performance measures into context (e.g., severity, truck involved, number of lanes blocked).