First-generation traffic preemption systems were primarily designed as optical-style systems. These solutions rely on sensors at each intersection being triggered by strobe light emitters on emergency and transit vehicles. While these initial types of installations were a step in the right direction, they offered little flexibility and came with a variety of challenges.
With advancements in technology, many cities, public safety, transit, and transportation departments are moving away from original, optical-based systems and to the new and more intelligent GPS-based preemptions systems.
Optic-style vs. GPS systems
The installation and maintenance of an optical-style preemption system is a complex process. Because this method requires a clear line of sight, the sensors can be cumbersome to install and need to be cleaned and re-adjusted frequently. Often, the wind can blow the optical detectors off alignment, requiring physical inspection, manual testing and readjustments on location.
In contrast, cellular based GPS systems are far easier to install and maintain. They only require two antennas to be installed in the intersection cabinet and a small, dual antenna, piece of equipment for each vehicle. Additionally, a central system can be used to view the data and access the preemption information – with instant access to reports highlighting response or bus route times and real-time data. Cellular based GPS systems do not require physical testing since they are continuously monitored and can be adjusted or upgraded remotely through the cellular connection.
Smart ways to begin the upgrade process
Upgrading to a GPS based preemption system can easily be done in stages and does not require a simultaneous update to every intersection. The two types of systems are able to work side-by-side during the transition so it can be done gradually over a given period of time.
Many agencies choose to begin the upgrade process with the key corridors. Most often the process starts at the intersections closest to the fire station and then moves to intersections that are the typically the most congested, while other agencies with transit applications consider heavy bus routes. Upgrades to these two strategic areas can make a marked improvement in response and route times. As funds become available, other intersections and congested routes can be upgraded.
With each addition, the agency will gain a greater benefit from the use of the system. Once the complete system has been fully upgraded to a GPS-based preemption system, many agencies see improved response times, fewer accidents, reduced liability and increased bus ridership with fewer buses on the same routes contributing to improvements to congestion.
