One culvert that has seen use by animals is 17 feet high and 47 feet wide, with Mill Creek, a small tributary of Rock Creek, flowing through one side. Much of the culvert is dry, covered with stone dust and gravel. Larger rocks lie along the walls, allowing smaller animals to dart from the shadows of one boulder to the next. Trees and shrubs were planted at the mouths of the culvert, so animals have cover while approaching or leaving.
"It's amazing how adaptive wildlife are," Shreeve said, "as long as they've got the essentials."
Tall fencing along the highway will give wild animals wanting to cross no choice but to go through the culverts.
Officials also are beginning to take precautions on older highways. The state has erected tall fencing along a stretch of Interstate 68 near Friendsville in Western Maryland, and posted signs warning motorists about wildlife in other spots where there have been multiple crashes in recent years.
The measures are meant to cut down on collisions with black bears as well as deer. Last year, 43 black bears were hit by vehicles, while 68 were shot by hunters, according to the Department of Natural Resources.
If the fencing near Friendsville reduces animal-vehicle collisions, state crews might put up more along I-68, said William Branch, an analyst in the SHA's environmental design branch.
Such measures can seem like luxuries when government budgets are squeezed. Fencing off just 3.5 miles of I-68 cost $878,000. Installing oversized culverts like the ones on the ICC can cost $500,000 or more each. In Montana, where motorists must contend with the likes of elk and grizzly bears, officials spent $1.8 million to build a dirt-covered animal overpass on one accident-prone stretch of highway near Missoula.
"It's not a cheap proposition," acknowledged Gates, the UM wildlife ecologist. But he said the costs should be weighed against the potential deaths, injuries and vehicle damage from collisions with wildlife. "What's a human life worth?" he asked.
Beyond human safety, some suggest it's the price to be paid if society wants to keep wild animals in a landscape increasingly crisscrossed with roads.
"It's about how you value wildlife," Shreeve said.