The Phantom Tollbooth
The high-tech secrets behind automated highway toll systems
The idea behind automated highway toll collection is simple: A car with a transponder passes through without slowing down, and a radio sensor charges the owner's account. The system reduces congestion and emissions, and more importantly, makes roads safer, since traffic flow remains steady.
But it’s not always that easy. What happens when drivers swerve across lanes or try to trick the system by obscuring their license plates? What about speed demons who tear through the toll zone, thinking they're too fast for the cameras to catch?
To ensure accurate toll-taking – and to beat the cheats – highway authorities are increasingly turning to multiple layers of technology that can scan a vehicle's shape, count its axles, and spot altered license plates. Raytheon's All-Electronic Tolling System, which brought highway-speed, open-road tolling to Massachusetts in October, does all that — a versatility that the system's developers say is its greatest advantage.
“It’s the integration of all these pieces,” said Mark Desmarais, Raytheon’s head of business development for highway transportation systems. “The sensors collect all the information. But then we provide the systems engineering, the brains, the electronics and software that interpret that information that put it together into a useable format that creates a very accurate toll zone transaction for each vehicle.”
The All-Electronic Tolling System, now used in more than 360 toll zones worldwide, tracks vehicles using a series of intertwined, high-tech tools. Sensors built into the pavement sense the vehicle coming and tell the first overhead camera when to capture the front license plate. A radio device sends a signal in search of a transponder, which answers and tells the system to charge the car owner’s prepaid toll account.
If there is no transponder, the system takes color photos of the vehicle, including front and rear license plates, then uses registry records to identify the owner and send a bill. If the driver has a transponder but forgot to bring it, the system takes the plate images, recognizes the vehicle is signed up for automatic tolling and debits the account accordingly.
Ground sensors follow the vehicle through the toll zone, tracking its movement, triggering a second camera to capture the rear license plate, and telling a special scanner to produce a computerized image of the vehicle's size and shape.
Having multiple forms of imaging data comes in handy, Desmarais said, in case one camera fails or in cases where a vehicle changes its size and shape during transit – for example, a truck that enters the toll road with a trailer but then drops it at a rest area and continues on with nothing in tow.
The ground sensors can even tell when a vehicle changes lanes. If a car enters the toll zone in the right lane but moves to the center lane halfway through, the sensors tell the cameras the car has moved and that the center-lane camera should take the rear-license plate photo.
The All-Electronic Tolling System can even learn to read bent or otherwise illegible license plates, with some human help. Plate pictures that the software can't read automatically are sent to an image reviewer. That person uses the readable parts of the plate, combined with the vehicle's make, model and color, to check registry records, identify the car in question and enter the information into the system's image database.
The next time the system sees that plate, Desmarais said, it will recognize the car automatically. That technology can also be used to help thwart toll evaders who alter or obscure their plates.
Raytheon entered the open-road tolling market in 1997, installing its first system in Toronto, Canada. Similar systems are up and running in Florida, Texas, and Virginia, as well as in Israel and Chile.
“It’s an area that is a high-growth market right now,” Desmarais said. “One way states are able to build new infrastructure is to assess new tolls. The most cost-effective way of doing that is all-electronic tolling, which is our specialty.”
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