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Behind the lens: How photo enforcement really works

In 1880, two brothers discovered that an electrical current could be produced by applying pressure to some crystals.

Maybe Pierre and Jacques Curie thought their discovery would lead to the light switch. But a modern-day speed trap was probably far from their minds.

But the piezoelectric effect, as it’s known, now lies at the heart of just about any fixed photo-enforcement system. Piezo sensors under the road can determine the speed of a car as it passes over them. Too fast and, flash, cameras capture the driver and rear license-plate.

It was an idea that bore fruit some 107 years after the Curies’ discovery. Another pair of brothers, James and Adam Tuton, sold the town of Paradise Valley on setting up a photo-enforcement system. It was the first such system in the United States.

“They only had four police officers on duty, and at any one time, they were all doing traffic,” says James Tuton, president and CEO of American Traffic Solutions. Adam is executive vice president and chief operating officer.

Paradise Valley officers could focus on bigger fish.

Since then, photo-enforcement has spread across the country. Most states have it, in some form, though few have embraced it as readily as Arizona and its municipal subdivisions. State highways alone have nearly 80 fixed and mobile units ready to flash lead-footed motorists.

And there’s competition. The Tutons’ Scottsdale-based business now shares the road with Redflex, an Australian company with U.S. operations in Phoenix.

Their setups are commonly known as photo-radar, though that’s only half correct. Usually only the mobile units use radar to determine speed, the same way radar guns clock Randy Johnson’s fastball. Fixed systems use below-pavement sensors. At intersections, there’s an added bonus; they can catch red-light runners.

With the growth of photo-enforcement has come a chorus of complaints. Opponents say it is an unconstitutional infringement on privacy. The companies themselves, citing opinion polls, say the public supports photo enforcement.

One thing is certain. It works on the principle of negative reinforcement, akin to delivering a mild shock to a lab rat.

Larry Scott is assistant police chief in Paradise Valley, a job he’s held for nearly five years. Before that, he spent 30 years as an officer and police chief in suburban Chicago.

“I had no knowledge of photo radar until I came to Arizona,” Scott says. “The primary purpose of photo enforcement is to change driver behavior. It’s definitely changed my behavior.”

The part that gets everybody’s attention is the flash of the camera. But that only occurs if the sensors pick up a speeding vehicle.

For each fixed system, two sets of piezoelectric sensors are embedded in the road. The rectangular cutouts in the pavement are usually visible. The speed is determined by the time is takes the car to travel from one set of sensors to the other.

“It’s time over distance,” Adam Tuton says. “It’s a known distance apart. It’s very accurate,” he says.

By accurate, he means the photo-enforcement clocks are tied by a network to the official timepiece at the U.S. Naval Observatory in Washington.

But the setup does more than register a car’s speed. The system’s computer has a database of wheelbases. The car in the picture can be matched with the wheelbases for known vehicles. A Chevy Tahoe on camera should match the wheelbase measurements for a Chevy Tahoe, not a Smart Car.

If there’s a match, Tuton says, “We know it’s the same vehicle.”

Red-light cameras use embedded sensors as well, and not just the piezoelectric type. Another type generates an electromagnetic field, says Tony Parrino, director of field services support for Redflex.

As the vehicle enters the field, Parrino says, “it changes the lines of flux.”

Drivers won’t notice electromagnetic lines of flux, unless they speed through on a red light. Then the telltale flash of the camera will haunt them for the next three blocks.

The sensors pick up vehicles likely to run a red light before they reach the intersection. The flash occurs when vehicles cross a red bar, usually just beyond the inside line of the crosswalk. Cameras capture the driver’s face and license-plate. In addition, a 12-second video is recorded.

The video might help get a driver off the hook for a right-on-red turn, James Tuton says. A slow-rolling turn might trigger a camera flash. But slow-enough and the ticket might be tossed.

“Without video, you wouldn’t know if it was slow or fast,” James Tuton says.

The photo and accompanying data are stored as an encrypted file in a nearby data-storage box. It includes information such as time and location. The information is periodically uploaded to a secure server.

As for the mobile units, operators use yardsticks to make sure the vans are perfectly parallel, or nearly so, to ensure the accuracy of the radar, Parrino says. A two-inch misalignment could mean a 1 mph loss of accuracy, he says. The radar is set at an angle to gauge vehicle speed in one or more lanes.

A speeding car will be picked up as it enters a cone-shaped beam. As it reaches the beam’s center, a rear-mounted camera flashes. A front-mounted camera takes a picture of the vehicle and its license plate as it speeds away.

Thousands of photos and accompanying data can be stored conveniently on computers. James Tuton remembers the old days, before digital cameras.

“We needed a thousand people just to retrieve the film,” Tuton says, adding that every field office had its own darkroom.

Even as technology has gone digital, the concept remains the same. Pictures of the driver and license are paired with data showing a violation. Most states, however, require only a photo of the license plate. They hold the car’s registered owner responsible, no matter who’s driving.

In Arizona, it’s the driver’s fault. So nailing down driver ID is a big part of photo enforcement. Valley centers for Redflex and American Traffic Solutions handle photo enforcement “touches” nationwide. Technicians at cubicles examine photos and data on computer screens. Generally, the photo and incident information go through at least three sets of eyes before it is deemed a good a ticket.

Identification is made through comparison with the driver’s license photo on hand at the state Motor Vehicle Division. MVD supplies the name of the vehicle’s registered owner as well. If everything matches, it’s an easy call. The citation is sent to the registered owner. And the driver is expected to pay up.

But often it’s not so simple. In Paradise Valley, for example, about 20 percent of the tickets aren’t processed – often because the driver can’t be identified. In some cases, the license plates can’t be read.

In many cases, jurisdictions that use photo enforcement give citations a final screening. The Arizona Department of Public Safety assigns officers to give photo-enforcement tickets on state highways a final seal of approval before they go in the mail.

The filtering process – the vendors and law enforcement agencies – lets very few bad tickets get through the system.

“We operate with zero tolerance for error,” James Tuton says.

A whole industry of critics, however, has sprung up to question the accuracy of photo enforcement. One Web site, camerafraud.com links to an electronic clipping service that specializes in articles about photo enforcement gone bad. One article, citing a Channel 3 news report, said a black man was sent a citation showing a white man at the wheel.

While mistakes can happen, judges, prosecutors and even defense attorneys say it’s difficult to challenge the system in court. Art Attona, Tempe Municipal Court commissioner, cites one case he tossed out. The car captured by the “face” camera didn’t match the car captured by the rear camera.

“There was a defect in the state’s evidence,” Attona says.

Sometimes the driver as photographed and the defendant appearing as a witness are obviously not the same.

“The defendant wins,” he says.

But wins like that are rare. Most court challenges, Attona says, don’t involve the technology of photo enforcement, but the vagaries of Arizona speed law. Except for the 15 mph school zone, there is no absolute speed limit, despite what the signs say. A motorist’s speed must be reasonable and prudent, according to the road conditions.

Photo enforcement citations provide wiggle room. Most, if not all, Arizona jurisdictions set the violation at 11 mph over the posted speed limit. But judges might give leniency to a motorist going 12 mph over the speed limit at 2 in the morning, when the road is likely to be clear and there’s little or no traffic.

Most people, it happens, challenge photo enforcement on the grounds that they were going with the flow of traffic. But technology continues to trip them up.

“There’s a document called a scattergram,” Attona says.

It’s a five-minute snapshot of all vehicles that have rolled past sensors. It shows the speed of each along a timeline, two-and-a-half minutes before and two-and-a-half minutes after the driver who was flashed. Attona says most scattergrams he sees show the flow of traffic clustered around the speed limit. The violator often stands out as a lone rogue clocked above the 11 mph window.

Attorney Karl Mueller of Higley specializes in traffic defense. He says the scattergrams often conflict with common sense.

“I’ve always had a real suspicion of those scattergrams, because they don’t match with reality,” Mueller says. “We know driving on the freeway – that’s just not plausible.”

Mueller himself no longer tries to contest photo-enforcement tickets on the system’s technology.

“All I did was aggravate the judge,” he says. “They don’t want to hear anything about some kind of technical defense.”

As city attorney for Prescott Valley, Colleen Auer works the opposite side of a courtroom. But she agrees with Mueller on his point that defendants rarely try to challenge photo-enforcement tickets on the technology.

Prescott Valley installed speeding and red-light systems – mostly on U.S. 69 – in late 2006 and early 2007.

“Initially, there were challenges about the equipment and how accurate the sensors for the fixed system were,” Auer says. “And with the mobile van, people were concerned that the equipment was not functionally accurate.”

But the technology has stood up to the challenges.

Redflex and American Traffic Solutions say they regularly check the accuracy of their systems. One test is done by taking random photos of motorists who aren’t speeding, just for comparison.

“It’s happened to me twice in Paradise Valley,” says Scott, the assistant police chief. “The speed limit’s 35 and I’m going 35. It’s a test flash.”

Occasionally, even those in charge get flashed. James Tuton says last year he was driving his son to a movie. During a moment of inattention, he said, he entered an intersection on Scottsdale Road as the light turned red.

He paid the ticket. He must have known the odds of beating it.

But even as defendants fare poorly in courts, motorists still look for ways to beat the system. There remains a cottage industry for license-plate covers designed to foil the cameras.

They don’t work, says Adam Tuton, unless they completely obscure the plate. Then the driver runs the risk of getting ticketed by an officer.

Some motorists likely would do anything to avoid getting pulled over. And sometimes they get caught by a speed camera. DPS officers working the photo-enforcement desk will keep an eye out for speeders wanted by the law.

In one case, DPS photo enforcement officers helped to identify a bank robber, says Lt. Jeff King, head of the DPS photo-enforcement unit.

“If you’re going to rob a bank, don’t speed,” King says.

The American Civil Liberties Union doesn’t object to using traffic photo enforcement for legitimate crime fighting. But the fear is police will be tempted to go beyond that, says Alessandra Soler Meetze, executive director of ACLU of Arizona.

“I think that the cameras are likely to be abused through what we call ‘mission creep,’” she says. “They start expanding the power of these cameras, and that’s where privacy begins to suffer.”

But law enforcement agencies and the vendors say they’re focused on the mission itself – changing driver behavior and making the roads safer. Wherever these systems are installed, they say, accidents and traffic fatalities have dropped.

Auer of Prescott Valley says crashes on U.S. 69, where it cuts through town, have gone down by 20 percent.

“This highway was known as blood alley,” she says.

Law enforcement agencies say the roadside cameras free up officers to deal with more serious crimes. Scott of Paradise Valley says there’s one thing photo enforcement can’t do that a cop can. Provide that personal touch.

“There’s the one drawback of the technology,” Scott says. “It takes out the human element. Here’s your ticket. Right or wrong, you go to court.”

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