Wednesday, May 12, 2010

Great Traffic Lights ... in Quincy, MA

This article in The Boston Globe is fantastic because it makes the operation of traffic lights understood. The technology and operational settings are complex. And the benefits can be tremendous, as the excerpt below indicates.

Not every community’s traffic lights operate as well as Quincy’s. Some communities lack the technology, even though the city’s is more than 20 years old. Others lack the personnel. But for those that prioritize traffic signal management, the benefits are numerous, Gillon said.

By platooning groups of cars, fewer vehicles get stopped at red lights, reducing idling emissions by as much as 20 percent, Gillon said. Extending green lights to allow 18-wheelers to pass through intersections — which Quincy does by use of surveillance cameras — likewise helps the environment.

Fewer cars stopped at intersections also can mean fewer rear-end accidents, as drivers’ attention tends to drift when sitting at red lights, Gillon said.

In the future, Gillon hopes to adjust his system to hold green lights for MBTA buses that are running behind schedule.

Best of all, with efficient traffic lights, everyone can get where they’re going faster.

“You’ve probably got 35,000 or 45,000 cars coming through here a day,’’ said Gillon, stopped at an intersection near the end of our journey. “If you’re saving even six seconds for all of them, that’s a lot, right?’’

Well, let's answer his question. Is it a lot?

About three million trips are made on a typical day on Oahu and we can extrapolate that there should be at least 60 million stoppages of vehicles in a day. Optimized traffic lights can reduce at least five (5) seconds for each stoppage, on the average.

These five seconds accumulate to 83,000 of vehicle hours of idling engines per day. This is like having 8,300 vehicles idle for 10 hours every day. So?

An average vehicle will consume about one third of a gallon per hour of idling, or one (1) gallon if it's a truck or bus. Let's stick to 0.33 gallons per hour of idle and 250 typical days a year. The rest of the year we assume no savings.

This comes out to nearly seven million gallons of saved fuel per year!

Further if you assume that the typical Oahu car is driven for 10,000 miles and has an average fuel consumption of 20 mpg, then it needs 500 gallons of fuel per year. Divide the 7,000,000 gallons of fuel saved by 500 and this 5 seconds of savings from traffic lights becomes equal to the permanent removal of 14,000 cars for one year.

That's more that any rail on Oahu will ever do. And you just thought that traffic lights were just three boring colors.

(A side point: On your regular commute you know the "long lights." You will save fuel and engine wear if you turn your engine off at those lights when you are caught at the beginning of a red signal. Hybrids do this regularly and get a big jump in their city MPG rating.)