Speed & Conditions
Posted limits assume good conditions, and Idaho's basic speed rule expects you to slow down when the road or weather is poor. Choosing a safe speed is one of the most important decisions you make behind the wheel.
Common limits
School zones are commonly posted at 20 mph when children are present, while some rural interstate sections in Idaho are posted up to 80 mph. Always obey the posted sign, which sets the legal maximum.
Basic speed rule
You must drive at a speed that is reasonable and prudent for actual conditions, even if that is below the posted limit. Traffic, weather, and visibility all affect a safe speed.
Adjusting to conditions
In rain, snow, fog, or blowing dust, reduce your speed and increase your following distance because traction and visibility drop. Brake gently and steer smoothly on slick surfaces.