Slow traffic with plentiful red lights and stop signs generally makes the District a tedious but relatively safe place to drive, but this year the number of people killed in traffic accidents has almost doubled.

There have been 23 fatalities so far in 2013, compared with just a dozen by this time last year. There was no apparent reason for the spike. No single incident in which several lives were lost that might account for it.

“The city has made significant strides in terms of improving traffic safety for all highway users — motorists, pedestrians, school children, the elderly, motorcyclists and cyclists,” said AAA’s John Townsend, who compiled the police department figures but was at a loss to explain the increase.

The number of deaths so far this year already exceeds the total of 19 fatalities for all of 2012. Last year’s death count was the lowest for the District in decades.

Nationally, traffic deaths increased in the first half of 2012, after declining to their lowest point in 60 years. For the six-month period, 16,290 people were killed, 1,340 more than during the same time frame last year.

The National Highway Traffic Safety Administration (NHTSA) is expected to release its fatality projections for the first six months of this year within weeks.