Traffic signal coordination is the timing of traffic signals so that a majority of traffic on the heavier-used road can pass through the intersection on a green light.
This has advantages:
- Relieves congestion
- Less waiting at lights
- Less pollution from idle autos
- Overall faster trips
The concept is that when the first cars in a large pack of traffic approaches a light, the signal should turn green right before braking would have to occur for a red light. If coordination works properly, all the lights on a street should turn green right before major groups of cars approach. This ensures traffic on primary roads don't have to stop every two or three lights waiting for side street traffic. Since traffic on the primary roads do not have to slow, congestion does not occur. Congestion occurs when a car in front brakes causing a chain reaction where everyone behind brakes as well.
This is a great system--in theory. In reality, things are more complex. When an automobile is on a primary road sitting at a red light, traffic from the other directions are filling the road ahead of the driver. This pretty much negates many advantages to traffic signal coordination. As long as build-ups occur further up the road, the signals will never be perfectly coordinated. Therefore, traffic stuck in the back of a pack will get caught at a red light eventually.
There is also a problem when two major thoroughfares intersect. Which road gets more privileges?
Also, the side streets tend to get neglected with these systems. They typically have to wait longer periods with coordinated setups.
Here are other disadvantages:
- Pedestrian crossings
- Left-Turn signals
- Side streets wait longer
- Off-peak traffic times
When it works, traffic signal coordination is a fantastic way in handling congestion in cities. However, the complexity of the world's roadways prevents major implementation from happening.