Traffic surveillance technologies play an essential role in incident detection, traffic management, and travel time collection. There are two basic types of traffic surveillance systems: road-based and vehicle-based. Road-based detection systems like inductive loop detectors have been a principal element of freeway surveillance and incident detection for many years. Similarly, video image detection and other roadside detection technologies have been used extensively to measure high-volume traffic conditions. However, advances in vehicle sensors and detection algorithms have given transportation authorities the opportunity to implement or enhance vehicle-based surveillance systems.

Vehicle-based traffic surveillance systems involve probe vehicles equipped with tracking devices, such as transponders, that allow the vehicles to be tracked by a central computer facility. Although not yet in wide use, these systems show promise of providing rich data on travel times and as a means to detect incidents. They can also be used to estimate flows and origin-destination patterns.

Moreover, vehicle-based technologies themselves have changed dramatically over the past decade, making the more dated AVL systems less attractive for collecting travel time data. During the past 5-10 years, GPS has become a popular choice of AVL system because many find it to be the most capable technology for collecting detailed travel time information. In addition, emerging studies of wireless geo-location have shown that cell phones may become an equally feasible method of automatic vehicle location.

The links provided are organized by road-based and vehicle-based technologies.