Traffic signal preemption lets buses glide through cities, saving time and energy – and, perhaps, the atmosphere.
Canadian city's broad avenues are filled with traffic, Calgary Transit's buses run nearly as fast as they do when the roads are empty.
That's because the city has equipped three bus routes with wireless technology that can pull off a trick every commuter has dreamed of: switching a red light to green on command. As these Calgary buses approach an intersection, the lights go from red to green or stay green just a little bit longer. The result is faster travel for riders, less pollution from idling and more fuel savings for the city. Jodie Marcyniuk, a transit priority engineer at Calgary Transit, notes that each of its transmitter-equipped buses saves 2,000 gallons of fuel and nearly 50,000 pounds of carbon dioxide emissions per year compared with buses on regular routes. (The calculations do not net out the extra gallons idled away by drivers on the cross streets.) "It works out beautifully," says Marcyniuk.
This technology comes with the grandiose name of "signal preemption." Ninety-eight metropolitan areas have installed it in more than 30,000 intersections, or one-fifth of all intersections with traffic lights in the U.S. Leading the way are Bellingham, Wash., Eugene, Ore., Boise City, Idaho and Syracuse, N.Y., all of which have installed the system on at least 90% of intersections.
Houston found that its preemption system has cut travel time for emergency vehicles equipped with transmitters by as much as 23% – an enormous difference for a patient in cardiac arrest. Faster emergency response times also allow cities to stretch precious capital budgets. Plano, Tex. was able to serve 7.5 square miles per fire station with signal preemption, compared with 5.6 square miles without it. By not having to build three additional stations, Plano saved $9 million in construction costs and $7.5 million in annual operating costs.
The signal preemption idea was born in the early 1970s, when 3M devised a system that let emergency vehicles change traffic signals with pulses of strobe lights (later, infrared light) transmitted to receivers mounted over roadways. The technology was slow to take off, as some cities found it difficult to integrate preemption with antiquated traffic-light controllers. But it worked. When St. Paul, Minn. installed an early signal preemption system, it reduced emergency vehicle crashes by more than 50%, despite population-fueled congestion in the years following the system's installation.
In 1979 3M revamped its technology – sold under the Opticom brand – to allow it to recognize two different priority levels: a high level for emergency vehicles, which could force traffic lights to change immediately and a lower level for transit vehicles, which could hold off changing the light entirely if changing the light to green would snarl traffic.
Hackers eventually got in on the game, using mail-order infrared transmitters to switch red lights to green. In 1992 3M added encryption codes to stop the monkeyshines. 3M sold its Opticom unit to Canadian private equity firm Torquest for $80 million last year. Torquest folded the technology into a privately held firm called Global Traffic Technologies, which has the lion's share of the signal preemption market. Its chief executive, Richard Sachse, has already expanded the company into new, traffic-strangled cities in the Middle East such as Dubai. The system there will at first be used to allow time-strapped sheikhs to zip across town. Eventually EMS vehicles will be able to as well.
The latest generation of Opticom gear does away with infrared in favor of a combination of cellular radio and Global Positioning System links, which can pinpoint a vehicle's location and speed. When a GPS-equipped bus approaches an intersection, it can, as before, take over the intersection's traffic light, but the computer can also calculate its expected time of arrival and decide either to extend a green light or shorten a red light. It also takes note of whether the bus' turn signal is on and can prepare a green turn arrow if the bus needs to head left or right. The preempted traffic light returns to normal operation within a cycle or two.
GPS-equipped buses can also tell traffic computers whether they are behind or ahead of schedule and whether they have passengers onboard (as calculated automatically by the buses' passenger counters). Empty buses and those running ahead of schedule have to wait at red lights like everyone else. "Fuel economy isn't helped when cross traffic is idling while it waits for an empty bus to go by," says Steven Arrington, the director of resource development at the Jacksonville, Fla. Transportation Agency, which has implemented a trial of the new technology. On the other hand, royal treatment for bus passengers can save the atmosphere just by getting people out of their cars.
Cities are also beginning to use their buses' location data to answer that perennial question of cranky commuters: Where's my stinking bus? Auckland, New Zealand has 730 buses talking to 174 intersections using signal preemption, and their conversations are listed on 180 on-street information displays showing buses' estimated arrival times. A system in Portland, Ore. features displays at nine bus stops, as well as an automated bus status line that fields a million calls per month.
The Opticom GPS system costs $5,300 per intersection and $3,000 per vehicle. Cities and states can pay for the gear by tapping the federal government's $40 billion annual highway trust fund or the $193 billion of pork apportioned in the transportation bill passed in 2005.
Fast-growing cities with sprawl problems, like Las Vegas, Phoenix and Denver, "are completely enamored of the density that intelligent bus transit enables," says Robert Puentes, a fellow at the Brookings Institution. Developers have taken note with big projects in Dallas and Portland, Ore.. It's amazing what a green light can do.