While that may not seem especially surprising, the study of accident records from 1989 to 1996 also provides telling commentary on how carefully park visitors heed posted speed limits.

Visitors' speeds, the study found, were less influenced by the posted speed limit than they were by the condition of the road: The more deteriorated the road, the more slowly visitors drove and the fewer animals died in collisions with cars - an ironic benefit of the disintegrating park roads that generate more visitor complaints than any other park issue.

"People tend to go as fast as the road allows them to go," said Kerry A. Gunther, a Yellowstone bear biologist who led the study. "Where we have the most road kill is where people travel the fastest. On our old, curvy, potholed roads, people slow down."

Federal highway standards generally favor straightening roads and cutting vegetation back to create wide "clear zones" on both sides of highways to improve visibility for drivers. But the study found that more animals than expected died along non-forested roads - that is, roads cleared of vegetation on both sides - apparently because such open terrain attracted animals to graze along the roads.

While only 32 percent of Yellowstone roads are considered non-forested, those sections of roads accounted for nearly half of the 939 large mammals - from bears to bison - killed by vehicles during the study.

The finding counters the conventional wisdom that there is a greater danger of colliding with wildlife along forested roads where animals can dart out of the woods and into traffic.

"When you cut trees back, you're basically creating meadows along the road, so animals will spend more time there and have a greater likelihood of getting killed," Gunther said.

With the results of the study in hand, park managers hope to maintain the rural and meandering nature of park roads scheduled to undergo $280 million worth of reconstruction and rehabilitation over the next 19 years.

"Wildlife is always factored in," said Yellowstone landscape architect Eleanor Williams, a member of the park team that oversees road work. "When you're trying to deal with Winnebagos and bicycles using the same roads, we need to make certain improvements for safety. But part of the nature of park roads is curvature and we're not going to change that."

Authors of the road-kill study suggested that roads designed to keep speeds at 45 mph or below would follow "the mission and mandate of the National Park Service to preserve and protect park wildlife while providing for the safety and enjoyment of visitors."

Radar data showed that along roads with posted speed limits of 35 mph or 45 mph, drivers traveled within 1 mph of the posted speed limit on average. On roads with a speed limit of 55 mph - the only one being U.S. 191 through the park's northwest corner, a commercial trucking corridor - drivers traveled an average of 16 mph above the posted limit.

New roads coax even more acceleration. The road-kill study compared average vehicle speeds along an old, deteriorated section of Yellowstone's east entrance road and a reconstructed section of the same road. Both carried a posted speed limit of 45 mph, but vehicles traveled an average of 5 mph faster on the new section of highway.

Rebuilding roads also leads directly to more wildlife deaths, the study found. In the three years prior to a 1992 rehabilitation project along Yellowstone's west entrance road, an average of seven large mammals died in motor vehicle accidents annually. In the four years following the roadwork, though, the average number of animal deaths nearly doubled to 13 per year.

Rangers also issued 60 percent more speeding tickets on the west entrance road following the road improvement project there.

Even the increased speeds and in wildlife deaths did not claim enough individual animals to threaten park wildlife populations. Elk were the most common large animal killed on park roads, with an average of 47 elk dying on the roads each year during the eight-year study. But that figure still represents less than 1 percent of the total Yellowstone elk population.

Accidents along roads annually claimed about 2 percent of the estimated 2,000 mule deer in the park and about 2 percent of the fewer than 100 wolves in Yellowstone during the study, but those deaths did not cripple either population. Wolf numbers in the park have continued to rise since the study, with more than 100 wolves now dwelling in and around Yellowstone.

Grizzly bears, black bears, coyotes, ravens, bald eagles and other species all benefit from highway collisions that claim wildlife by feeding on the resulting carcasses, the authors of the study said. Up to four different grizzly bears have fed on the carcass of a single road-killed bison in one day and other observations suggest road-killed wildlife is an important source of nutrition for carnivores and scavenging animals.