An Arlington, Va. school bus idles in the driveway of Wakefield High School, demonstrating special cameras that catch motorists who illegally pass school buses when the buses' stop sign arm is deployed. Officials in Maryland say they have seen a big jump in the number of drivers who illegally pass school buses. (Moriah Balingit/The Washington Post)

The number of Maryland drivers who illegally passed school buses that were stopped to let children on and off increased more than 50 percent in the past year, according to the results of a state survey released Tuesday.

The survey, based on violations counted on a single day in April, found 4,326 vehicles passed stopped school buses — ignoring their stop arms and flashing lights — compared with 2,795 in 2015.

The new figure came in well short of the highest ever counted — 7,011 violations in 2011 — but state officials described it as a troubling exception to what has largely been a trend of improvement from year to year.

They called on drivers to pay more attention.

“It is illegal to pass a bus with its stop arm extended and its lights flashing,” Karen Salmon, the state’s school superintendent, said in a statement. “It is clear that we have more to do as we all work to keep students out of harm’s way.”

There were 999 violations during this year’s survey in Montgomery County, up from 883 last year.

“There was a downward trend, and now we’re headed back up, which is disconcerting,” said Todd Watkins, director of transportation for Montgomery’s school system, the state’s largest. “Every occasion of illegal passing is a potentially life-altering tragedy for a student and their family.”

Watkins noted a new three-year effort in Montgomery to install safety enforcement cameras on each of the district’s 1,287 school buses. Using technology similar to that of a red-light camera, the bus-mounted devices capture images of violators and issue $125 tickets to vehicle owners by mail.

Force Multiplier Solutions, a contractor, is funding the $15 million initiative and will keep ticket revenue until the cost of the investment is recovered. The company then will split revenue with the county in later years, Watkins said.

“I hope this is a deterrent and we see the numbers go way, way down,” he said.

The total number of violations during the survey nearly tripled in Prince George’s County — from 230 last year to 658 this year — but was similar to its 2014 count of 669 violations. School officials said the county’s six-year average is 564; the county has 20 buses equipped with stop-arm cameras.

“Even one driver passing our buses is too many,” a schools spokeswoman said in a statement. “With our students back in school, it is important that motorists keep their eyes on the road and their minds on safety.”

State officials could not pinpoint reasons for the increase, noting that there are variables that could affect the count, such as better reporting of violators and differences in local traffic conditions on the April day selected for the survey.

Though the survey is not scientific — with bus drivers asked to record violations on their morning and afternoon routes — state officials said they view it as a snapshot of illegal activity on the roads. All of Maryland’s 24 school systems were involved, and three-quarters of Maryland school bus drivers participated.

“It shows that violations are occurring, and drivers need to pay attention to traffic safety laws,” said Bill Reinhard, spokesman for the Maryland State Department of Education.

The highest number of violations were found in the state’s large school systems; Baltimore County’s total was highest, at 1,002. By contrast, the city of Baltimore’s figure was 128, down from 224 a year earlier. Bus drivers in four small counties reported not seeing any violations.

Maryland officials did not have data on how many of the state’s school districts have bus safety cameras.

In northern Virginia, at least two school systems are awaiting final approval from the state to reactivate their school bus stop-arm camera programs, said Frank Bellavia, an Arlington schools spokesman.

Maryland state officials noted that Gov. Larry Hogan (R) recently released more than $500,000 in funds to local law enforcement agencies to help them enforce school bus safety laws.