August 4th, 2011

MOVING MORE PEOPLE

Optimize Mobility, by Catherine Higgins.

Today’s post is second in a series about traffic signals. Missed the first post? See it here.

Did you know that the first traffic signal was invented in Salt Lake City?

The device looked like a bird house and was controlled by a police officer on the side of the road. Today’s signals are equipped with detectors, computerized timing and variable phases. And the signal controller is a computer or a live person watching from a Traffic Operations Center miles away.

A young man poses by Lester Wire's first traffic signal. (Used by permission, Utah State Historical Society, all rights reserved.)

Modern innovations have helped traffic engineers manage traffic flow and reduce delay. Still, there are a lot of factors to consider when it comes to achieving orderly progression from signal to signal:

Directional traffic volume – Most UDOT roads are not busy all the time. Very heavy traffic volume often occurs only during morning and evening commutes. The most efficient way to deal with high volume directional traffic is to provide more green light time for commuters.

For roads that are busy outside of the standard morning and evening commute, other solutions, such as a CFI, dual left turn lanes or a Thru-Turn may be a good option when signal timing alone won’t help. UDOT will implement Flex Lanes on 5400 South in Taylorsville this year. 5400 South experiences heavy traffic volume during the morning or evening commute with very little to no delay the rest of the time.

Traffic patterns change – A variety of detection devices are used to see traffic and adjust the signal phases to accommodate traffic flow. “Modern signals are capable of detecting vehicles and pedestrians and can change based on actual traffic demand,” says Luker. Devices are usually mounted on signal arms or buried under or in the pavement.

Sometimes, timing needs to be adjusted to fit current traffic patterns. Many people call UDOT to report signals that seem to need attention. “In the city, almost everyone encounters traffic signals on a daily basis. If signals are not operating correctly, it causes delay and frustration, and often minor, inexpensive improvements can have a big impact.”

Detection can help signals work efficiently, especially on major arterial streets. “By having detection, the signal may see that there are no cars at the intersection in a particular direction,” says Luker. During the next cycle, the green phase can be made longer. “This is more efficient overall, because green lights aren’t being wasted, but if you are on a minor street you’ll have to stop more often.”

Special event traffic – Sports events or concerts can cause delay on an otherwise efficient roadway. Fortunately, most such events happen outside of the rush hour on evenings or weekends. TOC signal operators can anticipate events, like college football games, adjust the signals to give more green light time at the start or end of the event. While the event traffic is occurring, signal operators can observe traffic and make real time adjustments to expedite traffic flow.

Dual right turn lanes on east bound 9000 South – road users who take I-15 to the game get some extra help getting through the intersection. During normal traffic, the dual lane designation is off.

At State Street and 9000 South in Sandy, just north of the Soccer Stadium, variable lanes allow dual right turns when needed.

Allowing for transit vehicles – Trax Lines in Salt Lake County and the BRT in West Valley City require traffic engineers to make adjustments to signals to make the transit vehicles move efficiently along with automobiles. Signals on transit corridors are often timed to give priority to transit so the fewest number of people possible are inconvenienced. When train cars or busses reach an intersection, the phase order is interrupted to allow the transit vehicle to progress through the signal. After the transit proceeds, the signal plays catch-up.

Moving more people

UDOT is working hard to reduce traffic delay by making the current system work more efficiently and by increasing capacity where appropriate. The goal when it comes to signal timing is to move more people, not just vehicles.  Individual drivers can also make choices that can help save time, use less energy and reduce traffic congestion. Visit the TravelWise website to investigate some effective strategies like trip-chaining and alternative work schedules.

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Responses to “MOVING MORE PEOPLE”

  1. I never realized that there was so much information on the science and technology regarding traffic systems and devices. I am amazed by your site. Thanks for providing such interesting information.

    Zach

  2. Hi,

    This is a great read and I love seeing pictures of things like the early traffic signal at the top of the page. I think we take things like traffic signals too much for granted when we see them and don’t realize the technology needed behind them – apart from when they break down of course then we see the mayhem they cause !

    Great Reading,

    Thanks for Sharing.

    Phil.

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