Tuesday, September 9, 2008

Traffic Signal Synchronization

Many of the traffic lights on our roadways seem to be almost random. Sometimes they allow us to travel for several blocks before encountering a red light, but much more often they stop us at almost every intersection. The worst case is when a traffic light turns red shortly before a big platoon of cars nears its stop line. This should not be the case! To a traffic engineer, these occurrences are a red flag and demand a solution. Not only because random red lights are artificial bottlenecks, but also because they encourage red-light-running and other unsafe motorist behaviors which, in turn, may lead to crashes.

The easiest and most cost-effective way to deal with this issue is to synchronize the traffic lights, allowing cars to travel at least five blocks along main arteries without having to stop. As reported by the federal Department of Transportation, synchronization of traffic signals can and does yield tremendous benefits. A couple of examples, cited in the link above include: Texas, with a benefit-cost ratio of 62:1 (i.e.: for ever dollar spent, $62 was saved) and California, with a benefit-cost ratio of 19:1.

In summer 2008, the Institute of Transportation Engineers reported that Baltimore, Maryland spent about $750,000 to optimize and synchronize 800 traffic lights. Actual travel time runs were made with the old and the new traffic light timings. The improvements were huge and the cost-benefit ratio was 43 to 1.

An example of what synchronization would look like using King, University and Beretania streets in Honolulu is shown below.

The scenario above is similar to what exists today. The traffic signals are all uncoordinated, and, while some cars are able to make it through one or two intersections before being stopped again, the entire system operates almost randomly.

If the signals are properly timed, however...

As you can see, traffic travels from one end of the area to the other, almost without no stops, and much more smoothly than in the unsynchronized case.

The table below shows that the result of synchronization is a significant reduction in lost time, a significant reduction is the number of times vehicles had to stop. In turn, this results in a drop in the amount of emissions and fuel use.

Throughout urban Honolulu, with its over 500 traffic lights, the proper timing of intersection traffic lights can save over 50 gallons of fuel for the average car over a year. And ten times as much for taxis, buses and delivery trucks that are in traffic all the time. Fuel cost, fuel efficiency, congestion reduction and reduction of long idling times at traffic lights are critical elements in the operation of fleets. One of the largest fleets on Oahu is the TheBus with over 550 vehicles.