Scottish Natural Heritage (SNH) warned the risk of accidents involving deer and vehicles will rise when the clocks go back this weekend.
The change will mean rush-hour traffic will coincide with the time deer emerge to feed on grass verges near roadsides.
More than 7,000 collisions occur between vehicles and deer every year in Scotland, SNH said.
An average of 65 accidents result in people being hurt, with the estimated economic impact of vehicle damage and injuries said to be £7 million.
Warning messages will be posted on electronic signs across west and north-west Scotland from Sunday, including along the A9, A87 and A82, as up to 70% of accidents occur on A-class trunk roads or motorways.
Sinclair Coghill, SNH deer management officer, said: “From October to December, there is a higher risk of deer on the road as deer move down to lower lying ground for forage and shelter, with the highest risk from sunset to midnight and shortly before and after sunrise.
“We advise motorists to slow down and watch for deer crossing roads.
“Be particularly alert if you’re driving near woods where deer can suddenly appear before you have time to brake. If you do hit a deer, report it to the police, as the deer may be fatally injured and suffering.”
Dr Jochen Langbein, who oversees the national deer-vehicle collisions project, said the risk of colliding with a deer is about twice as high per vehicle-mile driven in Scotland compared to England.