For instance, female driving mileage rose 200 percent over the 16-year period, while male drivers increased their travel by 94 percent. That could be explained by more women driving to work today than in the 1970s.

With other factors still uncertain, Carol Popkin, an injury control researcher for North Carolina, hopes the government findings will focus more attention on female drivers.

For decades, researchers often bypassed female drivers in favor of higher-risk targets such as young men, said Ms. Popkin, chairwoman of a group studying female drivers for the National Academy of Sciences' Transportation Research Board.