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Bobby Sokhanvar
New member
Username: Bobby79

Post Number: 1
Registered: 06-2008
Posted on Wednesday, July 30, 2008 - 02:33 am:   

I saw a report on the news about long idle times at intersections. It seems like a problem in this city especially along 121 at night times. there are some intersections that cycle or take a long time to change when there is no traffic crossing. what is the city planning on doing? has having the signals flash yellow at night become an option?
 

Joel Fitts, Senior Traffic Engineer
Moderator
Username: Joel_fitts

Post Number: 6
Registered: 03-2008
Posted on Thursday, July 31, 2008 - 10:09 pm:   

Bobby,

The traffic signals along SH 121 are controlled by the City of Plano. However, I can say that, in general, operating traffic signals at frontage road intersections in flash mode is difficult because those signals are designed to direct traffic through them in a certain pattern. If they operated in flash mode, there is no guarantee that traffic would not build up in the middle of the frontage roads. In addition, at any intersection, with one direction flashing yellow, the other flashes red and all traffic on that approach has to stop. If traffic is relatively the same in all directions at night, flash mode would produce no net savings.

Within the City of Frisco, we do not operate any traffic signals in flash mode at night because of safety reasons and because most of our traffic signals are at the intersection of two major roadways (which are not good candidates for flash mode).

To minimize delay at night, our traffic signals operate in free mode, which means that they are not tied to a specific timing pattern and use their detectors to serve traffic as efficently as possible. When the signal detects traffic on one approach, it will give that approach the green as fast as it can. Even so, they sometimes approximate the operation of a flashing signal because they are programmed to rest in green on the major roadway (such as Preston Road) and only change to the minor approach when a vehicle is detected. This minimizes the times that vehicles on the heavier traveled roadway (such as Preston) have to stop at night, providing the most global savings in idle time.

During the day, the majority of our traffic signals are synchronized and operate in coordinated mode to provide the best possible progression of traffic in peak directions. Because our traffic signals are relatively new in Frisco, they do not need the equipment upgrades mentioned in the news report for older parts of the Metroplex. However, even with modern equipment, we have periodic programs where we undertake a major analysis to see if any retiming of our corridors would be beneficial. In fact, we will be conducting a couple of these studies in the fall using some funding similar to that mentioned in the news report.

Obviously, we cannot provide synchronized progression in all directions at the same time, so we cannot guarantee reduced idle time for individual vehicles in every situation. However, please know that our traffic signal timing procedures have the goal of reducing the overall idle time experienced by all traffic in total.

Joel Fitts
Senior Traffic Engineer
 

Mira
New member
Username: Josefina3

Post Number: 2
Registered: 09-2007
Posted on Thursday, July 31, 2008 - 12:03 pm:   

I experience the same problem. Often times along Panther Creek from 423 to the tollway I have to wait for lights while watching absolutely no cars go by. The wait can be as little as 10 seconds but sometimes extends to 30 seconds. That may not be bad for one intersection but several in a row not only wastes time but very expensive gasoline.
 

Joel Fitts, Senior Traffic Engineer
Moderator
Username: Joel_fitts

Post Number: 7
Registered: 03-2008
Posted on Friday, August 01, 2008 - 09:25 am:   

Mira,

I believe you wrote your post before I posted my response to Charles, so hopefully my response above will answer some of your questions.

Regarding your specific situation: Since Panther Creek Parkway has only been open a month, we are waiting for traffic patterns to stabilize in the area before we finalize the timing plans for the two traffic signals on Panther Creek. We may find that a different timing pattern would be more beneficial for minimizing delay (which will likely focus more on providing progression for the peak direction of travel).

As I said previously, we cannot provide synchronized progression in all directions at the same time, so we cannot guarantee reduced idle for every car in every situation. But we do work to reduce the overall idle time experienced by all traffic in total. Also, it is important to note that if a motorist is driving in the direction we are providing synchronized progression, they should be sure not to drive over the speed limit. If they do, they will arrive too early at the next traffic signal and have to wait at a red light.

Joel Fitts
Senior Traffic Engineer
 

Matt Hoffman
New member
Username: Mghoffman1

Post Number: 6
Registered: 02-2006
Posted on Friday, August 01, 2008 - 08:55 am:   

Couldn't ALOT of the idle time be reduced, by eliminating protected left turns when no cars are in the lane. It's very frustrating on Preston and Parkwood to wait as the traffic timing provides a protected left turn for a lane that has no cars in it. Also, how come so many traffic lights are beginning to provide protected left turns for only one direction at a time, instead of the traditional 2 sides at a time for left turns. The single side at a time is greatly increasing idle time at traffic lights.
 

Joel Fitts, Senior Traffic Engineer
Moderator
Username: Joel_fitts

Post Number: 8
Registered: 03-2008
Posted on Sunday, August 03, 2008 - 11:20 pm:   

Matt,

The decision to use protected only left-turn operations versus protected and permitted left-turn operation is usually based on safety. There are situations where sight distance is limited or the intersection geometry cannot allow for opposing left-turns to occur simultaneously (which would require us to provide the protected left-turn for only one direction at a time, as you describe).

The decision whether both left-turns should lead or one leads while one lags is a matter of trying to provide signal progression for the through movements. The use of leading and lagging left-turns is used to improve progression for the through movements in both directions along a roadway. While this operation may seem to increase the idle time for some vehicles, it reduces the overall idle time for all traffic passing through the intersection in total.

Joel Fitts
Senior Traffic Engineer
 

Bryan Fritchie
New member
Username: Hogcall

Post Number: 25
Registered: 06-2006
Posted on Tuesday, August 12, 2008 - 04:09 pm:   

I don't think you answered the first part of that question. Why does a protected left turn get a green arrow when no one is in that lane waiting to turn?
 

Perry Harts, Senior IT Strategic Planner
Moderator
Username: Perry

Post Number: 22
Registered: 06-2002
Posted on Wednesday, August 13, 2008 - 08:42 am:   

There are occasions where the turn arrow is used to gate traffic. If the traffic was released without the arrow, they would arrive at another red indication downstream because the platoon would arrive 7 to 10 seconds too soon. We do hold traffic at Wade and Preston for example to keep the flow from arriving at Lebanon too early and having to stop again. We used to have that operation, but stopping a larger platoon at Lebanon, we actually experienced more congestion there which we believe is due to the grade on the southbound approach. The grade reduces the rate at which the queue of vehicles were being discharged once the light turned green. After we made the change at Wade to gate traffic, the overall flow on Preston improved.

You could argue that Lebanon should be set to turn green earlier. However, this would result in losing progression along Lebanon and also for northbound Preston. Unfortunately the distance between signals varies and the speed varies as well.

Other times the arrow could be on due to a detection problem. If the detection fails, the signal then goes into a fail safe mode and will always bring up the arrow whether a vehicle is present or not. If you have concerns about a particular location, you can contact us at 972-292-5400.

Thanks
Brian Moen
Assistant Director of Engineering Services/Transportation

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