In Colorado the maximum speed limit is posted at 75 mph (121 km/h) on rural Interstate highways, even though Interstate 70 in the Rocky Mountains has a 65 mph (105 km/h) limit because of steep grades and curves and a 50 mph (80 km/h) limit at the east and west ends of the Eisenhower Tunnel. The maximum speed limit on other rural highways is 65 mph (105 km/h).
There are also basic prima facie speed limits in Colorado: 20 mph (32 km/h) on narrow, winding mountain roads, 25 mph (40 km/h) in any business district, 30 mph (48 km/h) in any residential district and 40 mph (64 km/h) on open mountain highways.
On certain stretches of rural highways, notably US-160 between Durango and Pagosa Springs and US-550 between Durango and Silverton, nighttime speed limits are in effect during peak migratory periods for area wildlife. Speeding fines are doubled when nighttime speed limits are in effect.