One slammed into a tractor-trailer, another collided with a driver turning left, a third clipped the bumper of a Mercedes while whipping through traffic on U.S. Route 50.

All three became statistics, among the 138 motorcyclists who died in Maryland, Virginia and the District in the first nine months of 2012, their names added to the 3,922 motorbikers who died nationwide during the same period.

In an era when overall traffic fatalities have fallen 23 percent, the number of motorcycle fatalities has doubled, climbing in 14 of the past 15 years. Preliminary data from the first nine months of 2012 suggest that they may have increased by close to 9 percent, as warm weather nationwide extended the riding season.

Henry Tharps Jr., 51, of Clinton hit a truck on Woodyard Road in May.

Sanford Thompson Jr., 50, of Capitol Heights collided with a car turning left from H Street onto Bladensburg Road in August.

Donnel Dandre McCoy, 29, of Bladensburg was racing at close to 100 mph with three friends when his Kawasaki touched the Mercedes on Route 50 in September.

“The fatality increase is disheartening,” said Troy Costales, immediate past president of the Governors Highway Safety Administration, a national coalition of safety officials that released the data Wednesday. “Every motorcyclist deserves to arrive at their destination safely. These numbers represent real people — they are family, friends and neighbors.”

When the final numbers are tallied for 2012, the group projects the total will be close to 5,000, at or near an all-time high. The nine-month numbers, when compared with 2011, showed the District unchanged with three deaths, an increase in Maryland of two, to 63, and a drop in Virginia of five, to 72.

Nationwide, 34 states reported more deaths, and 16 recorded fewer.

Good weather, higher gas prices and an improving economy that allowed for more motorcycle purchases were the most common explanations provided as states sent their data to the GHSA.

“Record-setting warmth,” reported Indiana, where the number of dead increased by 29.

“Economic recovery,” said Missouri, which recorded 20 more deaths.

“Price of gasoline,” speculated Wisconsin, where 24 more died than in 2011.

Although the weather, the economy and gas prices fluctuate, the safety group said there are three other reasons that are major factors in motorcycle deaths.

“The good news is that we know how to prevent crashes and the resulting injuries and fatalities involving motorcycle riders and their passengers,” said Kendell Poole, the group’s chairman and director of Tennessee’s highway safety program. “There are effective strategies that, when implemented, can make a difference.”

He said speeding, alcohol and reluctance to wear approved helmets result in unnecessary deaths.

The National Highway Traffic Safety Administration has estimated that 706 motorcyclists who died in 2010 would have survived if they were wearing helmets. In 29 percent of the fatalities that year, the rider’s blood-alcohol content was above the legal limit, and 35 percent of the cyclists were found to be speeding.

Only the District and 19 states — including Maryland and Virginia — require helmets for all riders. In Michigan, which repealed its helmet requirement last year, a University of Michigan study concluded that the state’s death count would have declined 21 percent had the law remained in place. Instead, the study found, it rose 18 percent.

“All of the trends with motorcyclist deaths are really going in the wrong direction,” Poole said. “This report is an urgent reminder that we must do more to address a problem that will only get worse with increased ridership. We are talking about 5,000 tragedies a year with no sign of progress.”