"This investigation determined that the speeds recorded for an extremely limited number of high-profile vehicles were excessive due to radar effects, most likely reflection off the large metallic surfaces of these vehicles," he said in an email. "Unfortunately, in these instances, the radar effects were not identified due to human error."

Gilligan said the company also "added in an extra quality-control step in the review process for tickets that are 30 mph over the limit to better prevent these anomalies."

That extra review would not have applied to two of the Mary Sue tickets, which wrongly claimed its trucks were going 47 mph.

Five cameras turned off

In August, five city cameras that have produced roughly 110,000 tickets suddenly stopped issuing any at all. One of them, on North Charles Street across from Notre Dame University of Maryland, was among the city's more prolific, yielding nearly a third of the combined total.

Asked to explain, city officials said they pulled the plugs after being challenged about how they define the "school zone" in which cameras are allowed.

State law is vague, saying a school zone can be anywhere within a half-mile of a school, whereas state guidelines for speed cameras say the devices should be placed only within 500 feet of a school, and only those serving kindergarten through 12th grade.

Baltimore's more liberal definition of "school zone" led to placement of cameras at colleges, across from hospitals with nursing students and near church preschools, The Sun found.

"We are especially concerned with the broad interpretation of how the city defines a school zone," said Averella, the spokeswoman for AAA.

It was complaints from Averella's group that led the city to shut down the five cameras and change its school zone definition to include only K-to-12 schools. The city maintains that all tickets issued at the five now-dark cameras, including the one by Notre Dame, are valid because they complied with the broad language of the state law.

"We came to the conclusion that, for the credibility of the program, we would be more conservative than we have been in terms of how we define school zone," said Murphy, the transportation official.

One of the five cameras fell into a different category. Since 2009 it had been cranking out tickets on Wilkens Avenue in Southwest Baltimore, placed there because of Cardinal Gibbons School. But Gibbons closed in May 2010. Murphy said the camera remained in use because another school, Seton Keough High, sits "about on the borderline" of the half-mile radius.

The city recently reconsidered and decided to turn off the camera because, Murphy said, people might wrongly assume it's there for the long-closed Gibbons.

Mixed record on traffic safety

The stated aim of the cameras has always been to improve road safety, not to raise money. And numerous studies conducted around the world have concluded that speed cameras do lead to slower driving, with fewer collisions and fatal crashes.

According to a recent analysis of 35 studies that was published in the Cochrane Review, which aggregates and analyses scientific research, drivers reduced their speed by up to 15 percent in areas where cameras were used, while crashes declined as much as 49 percent and the number of serious injuries fell.

"Anybody who studies this finds them to be effective in terms of reducing speeding," said Richard Retting, engineer for the Insurance Institute for Highway Safety. "The jury is in on that question."

City officials have reached the same conclusion. Before-and-after studies done by the city show vehicle speeds dropped at all but five of Baltimore's initial 48 camera locations, many of them sharply. And the cameras don't just reduce speeds near where they are placed but throughout the city, officials maintain, because motorists worry that a camera could lurk around any bend.

"Because we do have a lot of devices around the city, you can't just say, 'Oh, I know where they all are,'" said Murphy. "You have to obey the speed limit or at least stay within 12 mph pretty much everywhere, because you don't know."

But the numbers also show wild fluctuations at some locations and during some time periods, suggesting that forces other than mere driving habits are at play. A busy camera on South Caton Avenue, for example, logged about 3,100 tickets in April 2011, but more than 4,500 two months later. The number dropped to 1,600 later that year before climbing back above 2,500 several months later.