Traffic control is always a compromise

Because of a wide variety of users, traffic control is an ongoing compromise by authorities that control signs, signals and pavement markings. Think about it — traffic control would be much simpler if there were only vehicles to consider. But there’s a whole lot more. We must consider all users, including bicyclists, pedestrians, slow-moving vehicles like farm implements and horse drawn buggies — you get the picture.

Let’s take pedestrian crosswalk signals, for instance. There are fast walkers, slow walkers, like the elderly, and people with canes or walkers. So, how much time do you give pedestrians to cross a street or road? The answer isn’t as simple as you might think. Too much time, motorists complain. Too little time, pedestrians complain.

The more time for pedestrians the less time for traffic, and vice versa. The compromise here is the suggested cross time of 3 1/2 feet per second. That turns out to be a good compromise between slow walkers and fast walkers, enough time for all but the slowest pedestrians.

Another compromise is in 3-color traffic signals. Obviously, more time is allotted for the street with the more traffic, but the driver on the less busy street doesn’t want to wait any longer than he/she thinks is necessary, so traffic engineers must assign minimum and maximum times for each signal phase. Decades ago, signals changed at pre-determined times for each phase. Now, signals are computer-controlled, with either loop, video or microwave detection to “see” what vehicles are waiting in what lane on each leg of the intersection. At most intersections, the “green” will rest on the busier street or road until vehicles on another leg are detected, and upon a pre-programed time, the computer will change the traffic signal lights to allow the waiting vehicle(s) to proceed.

Speed limits are another compromise. Everyone wants a speed limit on their street or road but not on others. Speed limits are set with a multitude of considerations. Speed studies are also normally completed to determine the 85th percentile speed, which is the speed that 85 percent of free-flowing vehicles are traveling at or below. The consensus of traffic engineers throughout the country is that the appropriate value for a speed limit will almost always be that indicated by the 85th percentile speed to the nearest 5 mph. Pavement markings indicating passing or no passing is yet another compromise. Often drivers question whether it’s safe to pass where it is permitted or why it isn’t permitted when they think it should be. There are sight criteria that engineers apply to determine the proper markings. The compromise is to try to provide passing where possible but not at the expense of safety.

Highway costs are also an area of compromise. Does traffic warrant significant expenditures or not? Is a two-lane road adequate or do you need four lanes? Are guide rails necessary or not? Is a STOP sign needed or would a YIELD sign be appropriate? Are STOP or YIELD signs adequate or is a 3-color traffic signal needed? Thankfully there are warrants available that give a pretty good indication on whether a signal is necessary or not. As an alternative, perhaps a roundabout could be a solution.

There are many considerations for traffic control. That’s why engineering studies are almost always required before changes are made. It’s always a compromise.


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