WASHINGTON — More than two-thirds of young drivers and passengers killed in nighttime car crashes aren’t wearing seat belts, the government said Monday.

Seat-belt use rose to 82 percent last year — from 81 percent in 2006 — the government said. Twelve states had rates of 90 percent or better, led by Washington and Hawaii. Only three were below 70 percent: Arkansas, Massachusetts and New Hampshire.

But the news was hardly all encouraging. Sixty-eight percent of drivers and passengers between the ages of 16 and 20 who were killed in car crashes at night in 2006 were unbuckled, said the National Highway Traffic Safety Administration. During daytime, 57 percent of the young motorists and passengers who were killed were not wearing seat belts.

That portion of the study focused on 2006 data.

The problem isn’t just with teens. The percentage of unbuckled drivers and passengers who died at night is well up in the 60s through the age of 44. It declines to 52 percent for people 55 to 64 and 41 percent for those older than that.