VIDEO: Mesa traffic engineers and the city’s fire department are testing a GPS-based system for preempting traffic signals that could reduce crash rates and improve response times in the city. In certain areas, crews “get in a lot of congestion and, sometimes — while responding ‘code 3’ to an emergency — actually have to stop,” said Mesa Fire and Medical Deputy Chief Brian Yox. The city is testing GPS systems in two locations: Power Road between Southern Avenue & Guadalupe Road, Dobson Road between Southern Avenue & Guadalupe Road. The current system used in Mesa and most other Valley cities involves sensors on or near traffic signals and strobe-emitting devices on individual trucks that must be within visual view to prompt a signal change.