Nothing spoils the calm of an autumn evening drive like a 200-pound mass of flesh, fur and bones crashing through the windshield at 55 mph.

The Pennsylvania Game Commission is advising motorists to slow down during the hours just before dusk to sunrise to avoid collisions with white-tailed deer.

Deer-vehicle collisions increase at this time of year, when deer are entering the breeding season or "rut." Game Commission executive director Carl G. Roe said knowledge of deer habits can help motorists to avoid running into them.

"During the rut, deer are moving about more than usual," Roe said. "It's a time when deer become preoccupied with finding the opposite sex or staying a few steps ahead of rival suitors. It's a time when this summer's fawns -- left alone while does follow nature's calling -- sometimes naively wander into troublesome predicaments. It's a time, quite frankly, when deer don't seem to maintain the distance that typically keeps them from dangerously interacting with Pennsylvania motorists."

Often, motorists watching deer that have successfully crossed the road slam into another deer following behind.

"Deer frequently travel in family groups and single file," Roe said. "Just because one has crossed, doesn't mean the threat is over. Its crossing could be a signal that others may follow, which they sometimes do blindly."

When you see a deer cross, slow down and look back at the spot where the deer entered the road. During the rut, bucks may follow does with their noses to the ground, oblivious to the dangers of the roads they're crossing. Hunters, hikers and farmers tend to move deer more often this time of year.

In twilight and dark conditions, be aware of barely visible movements, headlights reflecting off a deer's eyes, and horizontal lines (which could be a deer's back) in a vertical forest. And take those "Deer Crossing" signs seriously.