Updated

WASHINGTON (AP) — The government estimated Monday that 45 million Americans are not buckling up in their cars, a poor habit that factors into thousands of highway deaths every year.

The Transportation Department released its estimate of seat belt use as it kicked off the annual "Click It or Ticket" campaign. The department said 84 percent of motorists wore their seat belts in 2009, an all-time high, but that still left millions of unbelted Americans on the nation's roads. Eighty-three percent were buckled up in 2008.

Transportation Secretary Ray LaHood said an average of 38 unbelted people a day are killed in motor vehicle crashes. In 2008, nearly 14,000 motorists not wearing seat belts were killed in motor vehicle crashes. Half could have been saved if they had buckled up, he said.

"Wearing your seat belt costs you nothing and not wearing one costs everything," LaHood said.

Statistics compiled by the National Highway Traffic Safety Administration found that those least likely to buckle up are teens and young adults, males, nighttime riders, motorists traveling on rural roads and motorists riding in pickup trucks.

Among states, Michigan led the nation with 98 percent of its motorists buckling up, followed by Hawaii with 97.9 percent, Oregon with 96.6 percent and Washington state with 96.4 percent. Fifteen states and the District of Columbia had a seat belt use of 90 percent or better.

Wyoming had the lowest rate in the nation with 67.6 percent, followed by New Hampshire with 68.9 percent and South Dakota with 72.1 percent.

Massachusetts, which had the nation's worst seat belt rate of 66.8 percent in 2008, showed the largest improvement among any state, raising its belt rate to 73.6 percent. Kentucky also made strides, improving to 79.7 percent in 2009, compared with 73.3 percent in 2008.

The "Click It or Ticket" campaign is running through June 6. More than 10,000 police agencies around the nation will enforce seat belt laws surrounding the Memorial Day holiday. The message will be reinforced with $8 million in national advertising, which began May 17.