Traffic Signal Preemption - Vehicular Device Types - Global Positioning System

Global Positioning System

With the advent of widespread Global Positioning System (GPS) applications came the introduction of a GPS-based traffic preemption system. These systems require software and a communications platform to determine where the activating vehicle is located, in which direction it is headed, which traffic lights should be preempted, and the ability for the central application to activate the desired traffic lights promptly.

Drawbacks of GPS systems include obstructions, single point of failure exposure, atmospheric conditions, and GPS satellite availability. In dense cities with tall buildings, GPS receivers may have difficulty obtaining the three required GPS satellite signals, required for triangulation to determine location. If the primary application is not installed with redundant hardware, a single failure on the primary system controller can disable all traffic preemption functions within the entire traffic network covered by the GPS-based system. Extremely heavy cloud cover or severe weather can also adversely impact the ability of the GPS receiver from obtaining the three required satellites. Additionally, recent concerns about the health of the GPS satellite network raise the possibility that the reliability of the GPS satellite system may degrade in the future.