Imagine this: It's a gorgeous spring day in Miami and you're thoroughly tempted to lower the top of your rental car and push the power pedal a little too hard in a bid to break free from the traffic crush on the Palmetto. But, though there may not seem to be a heavy police presence on the freeways on this particular day, you can be pretty sure that someone up in the sky is keeping a close eye on speeding vacationers and the massive traffic tailbacks they're trying to avoid.

Welcome to Florida, and aviation law enforcement from the state's Highway Patrol. It's one of the few states in the U.S. that employs aircraft to monitor speeders reckless drivers and, sometimes, soon-to-be felons fleeing a police pursuit (Nevada and Minnesota are among a dozen others). And if you never quite realized what those strange white lines on freeways mean, well, now you will.

States that Enforce Speeding Laws From the Air Include:

California
Florida
Illinois
Louisiana
Maine
Maryland
Massachusetts
Minnesota
Nebraska
Nevada
New Jersey
North Dakota
Ohio
Oregon
Pennsylvania
Texas
Viginia
Washington
Wisconsin

Flight Captain Matt Walker, the Florida Highway Patrol's chief pilot, says his job primarily involves monitoring motorists' speed between these painted white lines, which are placed a quarter-mile apart in frequent intervals.

Surprisingly, aviation enforcement doesn't involve radar: it's a straightforward stopwatch time over distance equation that allows a pilot to work out whether a driver has broken the speed limit. Captain Walker, having clocked a motorist driving too fast, then radios the speeding car's information to a waiting state trooper, or ground unit, who stops the car and issues a citation.

That is, if the driver stops. Sometimes, Walker says, they don't, a felony offense. But this is where aviation enforcement really comes into its own. In certain cases, rather than pursuing a fleeing motorist, which can be dangerous for all involved, an order will be given for the troopers to stand down but the pilot will still pursue the driver. Occasionally, the driver will head home, or even go shopping, completely unaware that his movements have been tracked from the air. Planes, after all, operate much more quietly than the helicopters often employed in other states in such pursuits. When the driver is quickly apprehended on the ground, usually they're shocked to hear they'd been tracked from high above.

"The troopers will back off and we'll follow the vehicle," Walker said. "When the person doesn't see the troopers' lights, he'll pull off and stop or he'll drive to his house. And as he's going into his house, the troopers are coming around the corner.

"It takes the fleeing portion out of the pursuit. Sometimes he'll still drive recklessly but the majority of the time he'll operate within speed limits if he thinks nobody is chasing him."

Walker says that a fleet of seven Cessna fixed-wing aircraft operates in the skies above Florida. The combined fleet delivers some 45,000 citations on average each year, and speed will be a factor in about 38,000 of these citations. The rest of the citations are made up of secondary factors, if the driver is drunk or not wearing a seatbelt, for example, or is driving on a suspended license. He says about 150 arrests are made each year where a pilot has spotted a clearly impaired driver, and aircraft enforcement results in the recovery of about 50 stolen vehicles annually.

"The primary use of aircraft is for traffic enforcement," Walker said. "The pilot has a stopwatch and observes traffic going down the roadway. He activates the stopwatch on the first line and calculates the average speed over the quarter mile.

"We'll say, 'the vehicle is a red pickup truck in the inside lane, number 5 behind you, off to your left now, now he's number 1. The trooper looks out his window and will pull in behind that vehicle. We confirm the time and speed and the pilot will return to the lines and do it over again."

The most challenging days for Walker and his team of pilots are busy holidays with heavy traffic and when the weather takes a turn for the worse. He says in those situations, or when a storm is looming, the fleet will be grounded. "We do not fly in inclement weather," he says.

Walker, who was born and raised in Florida, says that any prospective pilot must have logged at least one year as a regular state trooper and 500 hours of flight time and gained a commercial or instrument rating. He says many pilots were former civilian fliers who paid for their lessons out of their own pocket, although they can gain the qualification when they're going through the police training academy. Walker was a trooper for five years before he took to the skies, and now spends about five hours a day in the air. He also has to testify in court should a motorist decide to challenge a citation.

David Haenel, a defense lawyer at fightyourticket.com, has gotten to know many of the FHP pilots well in his long career fighting speeding tickets in Florida courts. He says he has won many cases challenging the basic equipment used to issue a citation -- including radio and the three stopwatches that pilots may use to clock a vehicle -- and discrepancies in the timing of an issued ticket.

He says that a pilot must prove that their stopwatches -- which must be of a certain brand -- have been calibrated in the last six months. He says a description of the car, its time and its speed must be written on the ticket, and that the citation's reliability must be proven beyond reasonable doubt. Which means that if there is a discrepancy between the time a pilot says he contacted the trooper and the time the trooper wrote on the ticket, even by a minute, Haenel has grounds to get the citation dismissed.

"First and foremost typically a client will tell me, 'I didn't see the plane in the air'," Haenel said. "But I want to know the locations of where the lines are, if the ticket is written in the appropriate venue [or county] if the troopers come from different stations, if the ticket is valid on its face."

"Every inconsistency goes in the benefit of the driver. The time on the citation is usually the most critical. If the pilot says 3.59, but the ticket's at 3.58, or 4.01, sometimes I don't even take these to trial."

Tread warily the next time you're tempted to put your foot down in Florida. You never know who might be watching. Or from where.