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Raj Gopal
New member
Username: Raj_gopal

Post Number: 2
Registered: 01-2009
Posted on Tuesday, January 13, 2009 - 09:28 pm:   

I have seen several collisions on Main and Legacy intersection…especially, with vehicles travelling North on Legacy & making left turn on Main. Can you share what’s being done to avoid them?

Joel Fitts, Senior Traffic Engineer
Username: Joel_fitts

Post Number: 24
Registered: 03-2008
Posted on Tuesday, January 20, 2009 - 04:46 pm:   


Due to the fact that the intersection of Main & Legacy spans a drainage ditch, it operates like a frontage road intersection with two sets of traffic signals. After a spike in the number of crashes at this intersection during the summer, we analyzed the data and it was apparent that some motorists were watching the far side signal indications rather than obeying the near side signal indications closest to them.

To mitigate this situation, the City reconstructed parts of the traffic signal in late September. Two of the span wires were replaced with mast arm poles in order to stabilize the signal heads so that louvers could be installed in them. The louvers are angled slats that make the green indication less visible to traffic on the upstream side of the widely divided intersection.

After making those improvements, there were no crashes at the intersection in October and only one traffic signal-related crash in November. (I do not yet have the data for December.)

Joel Fitts
Senior Traffic Engineer

Tracy Serio
New member
Username: Tserio

Post Number: 17
Registered: 08-2006
Posted on Monday, January 26, 2009 - 10:23 am:   

You may want to look at this timing of the lights in the intersection. I think that some of the reasoning might come from the north light not turning green and people just keep going through the light thinking it is green. I have noticed that most of the other lights around town are timed that once your go through the first light the next light turns green just as you hit it. I have seen many people run the north light at this intersection. Or they make a left turn at the north light when they do not have an arrow.

Joel Fitts, Senior Traffic Engineer
Username: Joel_fitts

Post Number: 25
Registered: 03-2008
Posted on Tuesday, January 27, 2009 - 06:08 pm:   


There are only a few possible ways to safely time a frontage road intersection so that traffic does not build up in the middle of it. One way makes sure that left-turns don't stop at the other side of the intersection, but it doesn't give as much green time to the through movements in all four directions. Another way maximizes time on the frontage roads, but requires that left-turns stop inside the intersection.

In the case of Main & Legacy, our choices for operating a set of frontage road traffic signals are further limited by the shorter distance between the two "frontage roads" of Main Street. Based on the configuration of the intersection and the amount of through traffic on all four approaches, we have chosen the timing method that gives more green time to the through movements rather than making sure each left-turn movement can be made without stopping. Otherwise, we would cause traffic to back up significantly on Main Street during the peak hours.

We will continue to monitor Main & Legacy for any signal timing tweaks that can be made. When Main Street is eventually widened to three lanes in each direction, we will gain additional flexibility in changing the signal timing at this intersection.

Overall, it is important to note that not all frontage road intersections in the area operate with the same timing method (along the Dallas North Tollway or SH 121). Therefore, motorists should always pay attention to the second set of traffic signals and not assume what they will do.

Joel Fitts
Senior Traffic Engineer

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