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.

If you drive Valley freeways during rush hour, you’re probably pretty familiar with ramp meters …

They’re the two-light signals positioned at most Valley on-ramps that tell motorists when it’s okay to head onto the freeway.

Ramp meters have been used in the Phoenix-Metro area for about the past 20 years and maybe you think not much about them has changed … but, actually they’ve recently become much more efficient!

Thanks to a project funded through the Maricopa Association of Governments (MAG), roughly 300 ramp meters have been replaced with units that use newer, smarter technology.

As ADOT’s Intelligent Transportation System Supervisor Chuck McClatchey explains in the video above, the older ramp meters were not nearly as efficient as the new models.

“The new controllers actually operate totally independent of each other, which, means you can have 15 cars in one lane, no cars in the other lane and it will give 15 straight greens and just maintain red on the left side,” he said. “The older technology would give two greens and then a green to the non-existent cars. … So you can see that it really was not that efficient.”

But how does the ramp meter “know” a car is ready and waiting to take off onto the freeway?

Well, there are actually sensors in the ground adjacent to the signals that can detect a car as it pulls up. The ramp meter will then give a green light and start metering back and forth between the two lanes.

The meters also get information from the mainline, or freeway.

If the mainline is free-flowing, then the ramp meter will put on as many cars as possible. But if the mainline traffic slows down, the sensors pick that up and the rate at which cars are given a green light slows down some to help relieve the congestion.

The system has something called a queue-loop located at the very top of the ramp, too. The queue-loop is kind of a manual override that senses when traffic is backed up on the ramp completely up to the top. If that happens, the loop is activated and the metering goes to the fastest rate until the ramp is cleared. Basically, it’s a safety factor that keeps traffic from backing up into the surface street intersections.

All these features add up and help make it a little easier for motorists to get where they need to go!