Idaho Driving Laws 2026: Speed Limits, DUI BAC Limits and Road Rules for the Permit Test

What speed limits apply in Idaho when no sign is posted? Idaho sets 25 mph in business districts, 35 mph in residential areas, 65 mph on highways, and 80 mph on some rural interstates. The DMV knowledge test is 40 questions with 85% required to pass. DUI: 0.08% adults, 0.02% under-21. Idaho headlights: required 30 minutes after sunset and when visibility drops below 500 feet. Hands-free cell phone use is required in school zones.

1. Speed Limits in Idaho

Idaho sets statutory speed limits by road type, and allows higher posted speeds on rural interstates (up to 80 mph where posted). The Basic Speed Law applies on top of these: you must drive at a speed that is "reasonable and prudent" at all times, even below the posted limit. Heres the statutory breakdown:

Key test point: Idahos Basic Speed Law requires driving at a speed that is "reasonable and prudent" at all times, accounting for road surface, weather, hazards, visibility, and traffic. You can be cited for driving too fast for conditions even if you are under the posted limit. Heavy trucks with 5+ axles over 26,000 lbs may not exceed 10 mph less than the posted interstate speed.

2. Right-of-Way: Open Range & Intersections

Idaho has a right-of-way rule you will not find in most other states: livestock and horses under controlled movement on public highways have the right-of-way. Beyond that, the standard rules apply, and Idahos knowledge test covers all of them. Right-of-way is always yielded, never taken.

4-way stop (all arrive at once)

Driver to the right

4-way stop (one arrives first)

Driver who arrived first

Roundabout / traffic circle

Vehicles already inside the circle

Emergency vehicles (lights/siren)

Emergency vehicle, pull to the right and stop

Pedestrians in crosswalk

Pedestrians always

T-intersection (no signs)

Through road traffic; drivers on the dead-end must yield

Yield sign

Cross traffic and pedestrians always

Merging onto a highway

Traffic already on the highway

3. Turns & Signal Laws

Idaho requires signaling at least 100 feet before any turn in business or residential areas, and 5 seconds on freeways and highways. Right turns on red are permitted after a full stop unless posted otherwise. Left turns on red are allowed from a one-way street onto another one-way street:

Right turn on red

Permitted after a full stop unless a sign prohibits it. Yield to pedestrians and cross traffic.

No right turn on red

When posted, you must wait for a green light before turning right.

Left turn on red

Only allowed from a one-way street onto another one-way street, after a full stop.

Left turn from two-way street

Start from the left lane; end in the left lane of the cross street.

Right turn

Stay as close to the right curb as possible; end in the right lane.

U-turns

Legal where not prohibited by a sign; must not interfere with traffic. Illegal in Idaho in a no-passing zone, on any curve or near a hill crest where you cannot be seen within 500 feet from either direction, or where a No U-Turn sign is posted. Solid pavement markings in the center of the road also prohibit U-turns.

4. Lane Rules & Line Markings

Idahos shared center turn lanes are reserved for left turns and U-turns from either direction, you may not travel through them or use them to merge into traffic. On multi-lane highways, you may not operate in the extreme left lane for a period of time that impedes lawful traffic. Heres the full breakdown:

Center turn lane (CTSL)

Used only to begin or complete a left turn; not for through travel or merging. You may travel no more than 300 feet in the CTSL.

Solid white line

Do not cross; marks the edge of the road or a lane that should not be changed.

Solid yellow line (your side)

No passing allowed.

Broken yellow line

Passing allowed when safe.

Solid + Broken yellow centerline

Passing allowed only on the broken-line side.

5. Passing: Idahos Speed Exception

Idaho has a unique passing speed exception: passenger vehicles, motorcycles, and pickups not towing may exceed the posted limit by up to 15 mph while passing a vehicle going below the limit on a two-lane road, if the posted limit is 55 mph or greater. This does not apply in work zones. Beyond that, Idahos standard no-passing rules apply:

• Only pass on the left, using the oncoming lane, when it is safe and legal.
• Do not pass within 100 feet of an intersection, railroad crossing, bridge, or curve where your view is limited. Look for the No Passing Zone pennant sign.
• The vehicle being passed must not speed up while you are overtaking.
• Return to your lane before coming within 200 feet of oncoming traffic.
• Never pass a stopped school bus with flashing red lights, this applies in both directions on undivided roads.
• You may pass on the right only when the vehicle ahead is turning left and there is a usable lane to the right. This movement shall not be made by driving off the roadway.

6. Following Distance

Idahos steep canyon roads, icy mountain passes, and long straight desert stretches all demand different following distance judgments. The 3-second rule is your minimum baseline under normal conditions, in bad weather on Idahos mountain roads, the handbook says to increase it several times over.

7. School Buses & Emergency Vehicles

Idahos school bus stop rules and the Move Over law are both tested on the knowledge exam. On undivided Idaho roads, all traffic in both directions must stop for a school bus with flashing red lights. Idahos four-lane exception: on highways with two lanes in each direction, oncoming traffic does not have to stop.

School Buses

• When a school bus stops with flashing red lights and an extended stop arm, all traffic in both directions must stop on undivided roads.
• On roads with a true median or physical barrier, only traffic behind the bus must stop, oncoming traffic may proceed.
• A center turn lane does not count as a divider. On 4+ lane roads without a raised median or barrier, all directions must stop.
• You must remain stopped until the red lights stop flashing and the stop arm is retracted.
• Illegally passing a stopped school bus in Idaho carries significant fines and points on your license. You must remain stopped as long as red lights are flashing and/or the stop arm is extended, until all children are clear of the roadway and the bus.
• Railroad crossings: School buses must stop at ALL railroad crossings, with or without passengers, even if no lights are flashing and no train is visible. This is a frequently tested rule.

Emergency Vehicles

• When you see or hear an emergency vehicle (police, fire, ambulance) with lights or siren: pull to the right edge of the road and stop. Do not block intersections.
• Move Over Law (Idaho): When approaching a stopped emergency vehicle or police vehicle with lights flashing, immediately reduce speed below the posted limit and proceed with caution. On roads with two or more lanes in the same direction, move one lane away from the emergency vehicle as soon as it is safe to do so.

8. DUI Laws & BAC Limits in Idaho

Idahos DUI law covers the full range, from standard 0.08% DUI through an enhanced penalty tier at 0.20% BAC or higher. Texting while driving is six times more dangerous than driving impaired, according to Idahos handbook. Refusing a chemical test? Thats an automatic one-year suspension before any court outcome.

9. Seat Belts & Child Seats

Idaho requires all occupants to wear safety belts and child restraints whenever riding in a vehicle equipped with them from the factory. Studies show seat belts reduce serious injury risk by 50% and are 60-70% effective at preventing fatalities in crashes.

10. Where You Cannot Park

Idahos parking rules include specific distances tested on the knowledge exam, plus a hill-parking requirement that is straightforward but frequently missed. Parallel parking requires wheels within 18 inches of the curb. Heres where you cannot park:

• Within 15 feet of a fire hydrant
• Within 20 feet of a crosswalk at an intersection
• Within 30 feet of a stop sign, yield sign, or traffic signal
• Within 50 feet of a railroad crossing
• On a sidewalk, in front of a driveway, or on a bridge
• In a no-parking zone or alongside a curb painted yellow or red
• Double parking (alongside a vehicle already parked at the curb)
• Headed downhill: turn wheels toward the curb. Headed uphill with a curb: turn wheels away from curb. Uphill without a curb: turn wheels toward the shoulder.

11. Driving in Bad Weather

Idaho winters are serious business. Snoqualmie Pass closes; Teton Pass ices over overnight; the Lewiston Grade gets chains-required conditions. And in summer, flash floods sweep through river canyons in minutes. Idahos handbook covers all of it, along with the unique open-range hazard where hitting livestock on the highway may make you liable.

• Headlights required from sunset to sunrise and when poor visibility makes them necessary. Use headlamps, not just parking lights, when lights are needed for driving in Idaho.
• In heavy fog, use low beams, high beams reflect off fog and reduce visibility.
• If you start to hydroplane, ease off the gas gently. Do not brake hard or turn sharply.
• In icy conditions, brake gently well in advance. Start slowing earlier than normal. Leave extra following distance.
• If your car goes into a skid, steer in the direction you want the front of the car to go. Do not overcorrect.
• Never use cruise control on wet, icy, or slippery roads.

12. Points & License Suspensions

Idahos point system uses a rolling 12 and 24-month window. Hit 8 points in 12 months and you get a warning letter; hit 12 and you are suspended for 30 days. Points can be removed by completing an ITD-approved Defensive Driving Course, once every three years, up to 3 points. Heres how it works:

Note: An ITD-approved Defensive Driving Course (DDC) can remove up to 3 points from your record, once every 3 years. A Traffic Safety Education Course (TSC) offered by law enforcement at the time of a citation can remove up to 4 points, but must be completed within 45 days of the citation.

13. Headlight Rules

Idahos wide-open rural highways and unlit mountain roads make high beams essential, but the law sets firm distances for when you must switch to low beams. The 500-foot oncoming / 200-foot following rule is the standard Idaho knowledge test question:

Key test point: Idahos rule is 500 feet for oncoming traffic and 200 feet for following, not 300. This difference from other states is a frequent source of wrong answers on the Idaho knowledge test. High beams must allow seeing at least 350 feet ahead; low beams must illuminate at least 100 feet.

14. Night Driving

Idahos rural roads at night present some of the highest wildlife-collision risks in the western US, deer, elk, and moose are most active at dawn and dusk, and a collision with an elk at highway speed is almost certainly fatal. On unlit stretches of US-26, US-93, and Highway 21, overdriving your headlights kills.

15. Cell Phones & Distracted Driving

Idaho bans texting while driving as an infraction, and the handbook makes the stakes clear: texting while driving is six times more dangerous than driving impaired. If you must use a cell phone, park in a safe place first. Hands-free devices without use of either hand are permitted.

Key test point: Idahos texting ban is an infraction, it does not add points to your record (unlike most moving violations), but it does result in a fine. A texting conviction only becomes a moving violation if you are operating a commercial motor vehicle. Hands-free use without physically holding the device is permitted. The handbook warns that texting while driving is six times more dangerous than drunk driving.

16. Railroad Crossings

Idahos Union Pacific and BNSF freight lines cross public roads throughout southern Idaho, the Magic Valley, and the panhandle. The ITD knowledge test covers exact stop distances and which vehicles must always stop at crossings. Never drive around lowered gates, it is illegal and the train will not stop in time.

Key test point: Never drive around or under a lowered crossing gate, it is illegal and extremely dangerous. Wait until gates are fully raised and all tracks are clear.

17. How to Drive a Roundabout

Idahos ITD handbook covers roundabouts and also two less-common intersection types unique to western states: the Thru-Turn (which prohibits direct left turns) and the Single Point Urban Interchange (SPUI, pronounced "spooey") used at freeway ramps. All three are tested. For roundabouts, the rule is always: entering traffic yields to vehicles already inside.

Key test point: The most common wrong answer on roundabout questions is thinking you have right-of-way when entering. You never do, yield to traffic already inside.