Traffic Signals

Often developers proposing a new subdivision or shopping mall hope to get the Road Commission to install a traffic signal at the entrance to their development to make it easier to get in and out. If there are already traffic problems in the area, frequently local residents will voice their agreement that what is needed to solve the problem is another traffic signal. It is as if signals are viewed as some sort of cure-all. They are not. Traffic engineers, in making a determination of whether a signal is or is not "warranted," refer to a manual of guidelines known as the Michigan Manual of Uniform Traffic Control Devices. This manual covers everything from signals, to pavement markings, to signs. Virtually identical manuals are used in every state. This manual identifies no less than 11 warrants that may be reviewed in determining whether a signal should be installed. The warrants that receive the closest review, however, are: minimum vehicular volume, interruption of continuous traffic, and accident experience.

Reviewing Traffic Signals


The first relates to whether there is sufficient traffic coming out of the entrance or side street in question to consider stopping traffic on the main road. The second relates to whether or not the traffic is too heavy on the main road for motorists from the side street to pull out. The last is an indication that the people are having enough difficulty getting out that right-angle accidents are occurring. All of us have experienced delays pulling out onto main roads from time to time, and the thought may have occurred to us that someone should put a signal at that location so we could get out more easily. But let's take that to the extreme. Let's say that everyone gets the signal they want. Now you are able to pull out of your sub or shopping center at a signal. You travel two or three blocks, only to have to stop at another signal at another sub or shopping center. And so it goes for your entire trip: stop and go every two or three blocks. Sure, the signals can be synchronized so that if you travel at a precise speed you can make all of them, but as soon as the car in front of you slows up to make a turn or the truck ahead fails to accelerate fast enough to make the next signal, you are out of sync with the signals. Consider how long it would now take you to get home from work or shopping.

Some people think that signals actually make the accidents go away. Actually it is possible to end up with more accidents after a signal is installed. However, the type of accidents change from right angle to rear end. If you were to obtain a listing of the top 200 intersections in the county where the greatest number of accidents were occurring each year, what do you think you would notice about those locations? You would find that all of them are signalized and have been for many years.

Why the Accidents?


Congestion and the fact that too often people who are frustrated at being delayed will take chances like running yellow lights, or even a red light. How many frustrated drivers would we have with signals every two or three blocks? The cost of installing a signal is often more than just erecting poles, wires and signal heads. Often road agencies are reluctant to signalize an intersection until the intersection can be widened to provide for a center, left-turn lane. If that is not done, the chances of rear-end accidents increases. Picture the situation where a driver sees a green light ahead and speeds up to make it, only to realize too late that the car ahead has stopped in the through lane (for lack of a turn lane) to make a left turn at the intersection. Keep all of the above in mind the next time you are having difficulty accessing a main road and you start thinking how nice it would be if someone put a signal there.