When a traffic light turns red, yellow or green in Cedar Park, it is guided by on-site cameras and engineers at the city's Traffic Management Center.
Each of Cedar Park's 51 intersections follows signal schedules preprogrammed by traffic engineers. Cameras transmit live feeds back to the center where computer software counts vehicles and tracks speeds, all to make traffic flow smoothly.
Engineers can watch the camera feeds, occasionally adjust signal timing based on traffic conditions and check reported problems, said Eric Rauschuber, Cedar Park director of utilities.
"The intersections don't communicate with each other," Rauschuber said. "The intersection controls itself based on preset parameters, but we can make adjustments to those controls."
Specific signal-timing schedules help regulate influxes of traffic throughout the day, Rauschuber said.
"We use coordinated plans in the a.m. and p.m. to try to get platoons of cars to stay together in one line," Rauschuber said. "When you're in the platoon, the likelihood of you hitting the next green is much greater in a coordinated plan."
Signals often work independently overnight or during other low-traffic periods, Senior Traffic Engineer Ali Mozdbar said.
"We just let them run free, first-come, first-served," Mozdbar said.
Many large cities have similar video-detection systems, Rauschuber said. The technology was developed in the early 1990s based on military technology used to spot tanks.
Cedar Park's first signaled intersection at Cypress Creek Road and Lakeline Boulevard had an older inductive-loop system. Still used in some cities, those systems rely on signals sent to the light from wires under the pavement.
Now all of Cedar Park's intersections use video detection.
Occasionally technicians must go out to the signals for repairs. Signal boxes use weather-hardened components, but cables inside them or the cameras can decay.
Signals may be hit with power failures or electrical shorts, which prompts flashing red lights on the signals and red circles on the engineers' screens. Recently a camera at Anderson Mill Road and West Whitestone Boulevard was not recognizing cars, and the signals were stuck in one programmed phase, Mozdbar said. Technicians repaired the camera.
Engineers test signal timing using computer models of vehicles in the city, but real drivers behave differently, Rauschuber said. Traffic engineers must either drive the roads themselves or watch vehicles on-camera to see how they respond to new traffic light schedules. Then they make changes to the model, he said.
Large public events, accidents and road projects also warrant manual changes to signal schedules, Mozdbar said.
Rauschuber said engineers are planning to change signal timing on East Whitestone Boulevard after Cedar Park's newest signaled intersection comes online at Whitestone and Market Street near the new Walmart.
Mozdbar said advances in the city's technology could allow signal-control programs to anticipate recurring special events or higher traffic during different times of the year. The city could also send traffic notifications to roadside signs or to drivers' phones, Mozdbar said.
Rauschuber said he regularly makes notes of needed signal upgrades when he is driving in Cedar Park.
"My kids will laugh at me cause I'll pull over and start writing something down if I see something," Rauschuber said. "It's fun, unless you're my kids."