ADOT works with cities on signal coordination

ADOT works with cities on signal coordination

February 2, 2012
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Nothing seems to slow a commute down like having to stop at one red light after another …

That’s why ADOT is working to synchronize some of its signals – a move that can help traffic flow a little more smoothly while reducing the type of stop-and-go traffic that can lead to congestion.

But wait … maybe you’re wondering how many traffic signals ADOT really has to worry about.

It’s true, this is the agency responsible for building and maintaining highways … and you don’t see any traffic lights out on the freeway. But you will encounter ADOT lights at freeway off-ramps and there are several state roads that have traffic signals.

Take Grand Avenue (US 60) for example … there are several lights on this stretch of road. Just last month ADOT worked to synchronize, or coordinate, the timing of the signals on Grand Avenue to reduce the number of stops that drivers make at red lights (maybe you’ve noticed a difference?).

The signals are synched to improve the flow of southeast-bound traffic during weekday morning commutes and to assist northwest-bound traffic during the afternoon.

ADOT is working with the cities of Phoenix, Glendale, Peoria, El Mirage, Surprise and Youngtown, as well as Maricopa County, on the project to coordinate traffic signal timing at a total of 36 Grand Avenue intersections.

Besides Grand Avenue, ADOT has signalized roads throughout the state including Route 66 in Flagstaff, Prescott Valley’s SR 69 and Tucson’s SR 77 … and they’re all synched.

To learn a little more about traffic signals and ADOT, we talked with ADOT Phoenix Maintenance District Engineer Tim Wolfe – he gets lots of questions about signals. We thought we’d share some of the most common questions along with the answers …

What speed should I drive to hit the green lights?
Wolfe says ADOT signals are synched to match the posted speed limit. In the case of Grand Avenue, that’s 45 mph.

How do the traffic signals know how to keep time with each other?
According to Wolfe, all the signals have a GPS clock installed. In the middle of the night each signal “talks” to the world clock and resets itself so each signal is exactly the same time.

If I miss a light, how long do I have to wait for the next green?
Wolfe says at the most you’ll be waiting half a cycle. A typical cycle is 90 seconds. On Grand Avenue it’s 130 seconds and in some places on Grand Avenue in Phoenix where there are six-way intersections, the interval is 210 seconds. So if you miss the green on Grand, expect a wait of anywhere from 45 seconds to 105 seconds depending on your location.

What sort of a difference does signal coordination make?
ADOT employees drove Grand Avenue before and after the signal synchronization in a vehicle equipped with a GPS device. They’ve gathered all the data and are analyzing it to get a precise look at the impact, according to Wolfe. However, even without the official numbers, Wolfe says drivers are noticing significant improvements on Grand Avenue.