Speed Limits, Following Distance and Lane Use
Speed limits, following distance and lane use
Idaho uses a basic rule: never drive faster than is reasonable and prudent for conditions, no matter what the sign says. Beyond that, the exam tests statutory limits, safe spacing and which lane you belong in.
Limits
- 35 mph in urban and residential areas unless posted otherwise.
- 65 mph on state highways that are not interstates, unless posted.
- 80 mph on rural interstate sections where posted.
- Obey school and work zone limits; fines can double in work zones when workers are present.
- The posted limit is a maximum for ideal conditions-rain, snow, darkness or gravel means slowing below it.
Following distance
Use the three-second rule: pick a fixed object the car ahead passes and count the seconds until you reach it. Add a second for rain, more for snow or ice, and extra space behind trucks or when someone is tailgating you, since you need room to slow gradually.
Lane use
- Keep right except to pass; the left lane is for passing and left turns, not cruising.
- Slower traffic keeps right on multi-lane roads.
- Use the center two-way left-turn lane only to begin or finish a turn, never to travel.
- On freeways, merge at or near highway speed and don't cross the solid gore area at an exit.
Worked example
The sign says 65 mph, but freezing rain is falling and traffic is moving at 45. Reasoning: the basic rule overrides the posted maximum, so driving 65 here is illegal even though it matches the sign-and 45 may still be too fast for the ice.
Traps that cost marks
Treating the posted limit as a target rather than a ceiling; camping in the left lane; believing a two-second gap is enough; accelerating hard to merge instead of adjusting to traffic flow.