WASHINGTON — Hawai'i drivers and passengers face three times the risk of being killed in a crash at night, when seat-belt use is lowest, than during the day, according to a National Highway Traffic Safety Administration study released yesterday.

Nicole R. Nason, the agency's administrator, said that to combat the problem and get more motorists to buckle up, the national "Click It or Ticket" seat belt campaign this year will focus on nighttime belt use.

The Hawai'i Department of Transportation and all four county police departments will run their seat-belt enforcement campaign from May 21 to June 3.

Hawai'i DOT spokesman Scott Ishikawa said Hawai'i, which was the No. 1 state in seat-belt usage in 2005, dropped to fifth place last year.

"We would like to somehow get those numbers back up, but it's more the fact that if we can get more people to buckle up, hopefully they will be safer in an accident," Ishikawa said. "Wearing a seat belt is the best defense for protecting yourself in an accident."

The new study on passenger vehicle fatalities showed that nationwide in 2005, more than 15,000 passenger vehicle occupants died in crashes between 6 p.m. and 6 a.m., and almost 64 percent of those killed were not wearing seat belts.

Of the almost 16,000 daytime fatalities, 47 percent were not wearing seat belts.

Since only about a quarter of highway travel occurs at night, the fatality rate per mile of travel at night is about three times higher at night than during the day, the study found.

In Hawai'i, the percentage of people not wearing seat belts killed in nighttime accidents was almost identical to the national average.

The state had 46 traffic deaths occurring at night in 2005, and 31 of the people killed — 68 percent — were not wearing their belts, according to the study.

During the day, 19 people died in crashes, with four not wearing seat belts. The time of day was not known for another four fatalities but all were wearing seat belts.

The agency said other survey data showed that nighttime seat-belt use is often 10 percent lower than the national average of 82 percent daytime use.

"It's alarming that fewer people are buckling up at night, a time when the odds of being killed in a motor vehicle crash triple," Nason said. "This year, law enforcement officials will be ticketing violators who are not wearing their seat belts, especially during evening hours."

Hawai'i's seat-belt law requires people in the front seats to use their seat belts and those 17 and younger to use seat belts in the back seat. The fine for not wearing a seat belt is $92.

The new study also found that alcohol and speed played prominent roles in nighttime fatalities, especially in Hawai'i.

Nationally, about 54 percent of nighttime fatalities had a blood alcohol content of .08 or greater, the legal limit for drunken driving. During the day, only 14 percent of the people killed in crashes had a .08 blood alcohol content or greater.

In Hawai'i, though, 33 of the 46 night fatalities — 72 percent — had a blood alcohol content of .08 or greater. Of the 19 daytime fatalities, two — 11 percent — had a blood alcohol content of .08 or more.

Nationally, 37 percent of the fatalities occurred in nighttime speeding-related crashes. Daytime speeding accidents accounted for 21 percent of the fatalities.

But speeding was involved in 61 percent of Hawai'i's night deaths — 28 people. During the day, 47 percent — 9 people — were killed in crashes where speeding was involved.

Reach Dennis Camire at dcamire@gns.gannett.com.