The Colorado Department of Transportation says 81 percent of adults in Colorado are using seat belts, an all-time high.
A study of personal vehicles was conducted in June and July by the Institute of Transportation Management at Colorado State University.
It showed that usage varies widely.
CDOT says 61 percent of pickup truck drivers and passengers in eastern Colorado used seat belts, while 87 percent of Front Range van drivers use them.
CDOT head Russell George says rising seat belt use has helped reduce traffic deaths.
He says more than 60 percent of those killed in crashes each year don't wear them.
Another study showed about 73 percent of Colorado drivers ages 16 to 20 wear seat belts.