No toll booths, no coins, no cash.

When tolls start at midnight on the Norfolk, Va., Midtown and Downtown tunnels, drivers won't see any of that. If they look up, what they'll see instead are cameras and antennas suspended above the road to collect the fees electronically.

There will be action below, too.

Sensors in the road will know, among other things, whether a passing vehicle has more than two axles. If it does, the system will know to charge that driver the higher, "heavy vehicle" toll rate.

"The system's smart enough to recognize you're pulling a boat," said David Caudill, administrator of VDOT's tolling operations division.

Boat or no boat, each vehicle will trigger a dizzying array of data collection points and computations in the second or so it takes to pass all that technology.

First, those sensors tell the system a car is coming. That tells the pizza-box shaped antenna on the overhead gantry to look for an E-ZPass transponder on the inside of the vehicle's windshield.

The antenna knows where to look because tolling systems are typically calibrated with all sorts of vehicle sizes and shapes, as long as the user has placed the transponder in roughly the spot near the rearview mirror, as instructed, Caudill said.

If the antenna sees a transponder, a computer will check to see whether it's associated with an E-ZPass account, and whether there's a balance to pay the toll.

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The transponder works on a radio frequency that basically sends a long string of numbers to the antenna, Caudill said. The microtechnology is encased in a plastic shell that's a little bigger than a pack of gum and runs on a battery expected to last for seven to 10 years.

If you don't have an E-ZPass transponder, or you left it in another car, the antenna will come up empty, prompting another sequence of events.

"It says, 'I've got an unknown vehicle with two axles. I'm going to take a picture of your license plate,' " Caudill said.

Elizabeth River Crossings, the private operator of the tunnels, has 50 cameras at the Midtown Tunnel and 30 more at the Downtown to capture images of license plates.

When tripped, the cameras take photos of the front and back of a vehicle. And those sensors in the ground? They can follow a car that changes lanes while all this is happening, so the front and rear photos will match.

Elizabeth River Crossings' computers then search for a license plate that matches the image. If need be, the company will go to out-of-state motor vehicle departments to find the registered owner, who will get a bill in the mail.

Online retailers hawk license plate shields that claim to thwart toll cameras. Elizabeth River Crossings said its equipment uses color and infrared technology that can negate most such attempts.

For toll road operators, it's a cat-and-mouse game to stay ahead of anti-toll camera efforts, which are also illegal, said Roberto Macias, a research scientist with the Center on Tolling Research at the Texas A&M Transportation Institute.

Image recognition systems on toll roads have improved significantly in recent years, with advancements in high definition cameras, lower costs and better software to make sense of the data, Macias said.

Some systems are so advanced they can create a signature for a car based on its unique characteristics, such as dents or scratches, he said.

Speed should not be an issue, either. In the early 1990s, electronic tolling systems were lucky if they could reliably read a transponder in a car traveling faster than 60 mph, said C. Michael Walton with the Center for Transportation Research at the University of Texas at Austin.

Now they're virtually 100 percent accurate with cars going over 100 mph - while changing lanes, he said.

That accuracy depends on the transponder being properly mounted, however. Holding the equipment up by hand and waving it around in hopes the antenna will read it can cause problems, Caudill said.

Then again, if a car with a registered E-ZPass account goes through and, for whatever reason, the antenna doesn't read a transponder, the system will learn, via the image of the license plate, that the user is a registered E-ZPass account. That account will still be charged the lower rate, as long as such instances are infrequent, said Leila Rice, a spokeswoman for Elizabeth River Crossings.

©2014 The Virginian-Pilot (Norfolk, Va.)