After months of 10-figure hauls, income from the District's controversial network of traffic cameras plunged in March to $2.6 million, a steep drop that did little to quiet the program's persistent critics.

Despite the puzzling plummet, the city remained on track to set another annual collections record from payments on tickets generated by the cameras.

According to statistics from the District's chief financial officer, the city raked in $2.57 million in automated traffic enforcement revenues in March. That's down nearly $18.7 million from February, one of the most lucrative months on record for the program.

It was also a significant dip from the District's March 2012 take, when the cameras added about $10 million to the city's coffers.

David Umansky, a spokesman for CFO Natwar Gandhi, said the city's financial experts did not know the origins of the decrease.

"We have no explanation for why the March [figure] is unusually low. It could be anything," Umansky said. "Month-to-month fluctuations cannot be seen as trends. Needless to say, we will be watching this closely."

The District logged a February-to-March decrease in camera revenues in 2012, when collections fell by $7.2 million, though city records show there's not always an end-of-winter decline. In March 2011, revenues jumped about 8 percent.

Despite the sudden slump, the District remains on pace to collect $104 million from the cameras during the 2013 fiscal year. That would easily surpass last year's $85 million haul, a record figure that emerged as a flash point in a litigious debate about the camera program.

D.C. Mayor Vincent Gray's office did not respond to a request for comment, but administration officials have said they expected revenues would fall because motorists would slow down to avoid tickets.

"People slow down, and the reason people slow down is they don't want to pay a penalty," Deputy Mayor for Public Safety and Justice Paul Quander said in December. "Money is generated, but if people would slow down, then it wouldn't be."

But a key metric for the program's success -- the number of traffic fatalities -- has climbed so far in 2013. Metropolitan Police Department data show the District had recorded nine traffic fatalities through Thursday, up from six at the same time last year.

The District in 2012 recorded its lowest traffic fatality figure in decades.

Lon Anderson, a spokesman for AAA Mid-Atlantic, doubted the March revenue figures in "a gotcha game for greenbacks" were an indication drivers had changed their habits.

"Do I buy that they changed their behavior $19 million worth in one month? No. I'd like to think that was the case," said Anderson, whose organization has criticized the cameras. "This number appears to be an aberration."