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's current handbook lists a maximum of 35 mph in residential, business, and urban districts unless otherwise posted; 75 mph on interstates unless otherwise posted, with 80 mph allowed where posted; 65 mph on state highways, with 70 mph allowed where posted; and 55-70 mph in other locations unless otherwise posted. The DMV knowledge test is 40 questions and you can miss up to six before failing. DUI: 0.08% adults, 0.02% under-21. Idaho headlamps and tail lamps must be lighted from sunset to sunrise and when poor visibility makes them necessary for safety. Idaho's hands-free law applies statewide, including during brief stops at traffic signals and stop signs.

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 violate the basic rule by driving too fast for conditions or by driving so slowly that you impede the safe flow of traffic. School-zone and work-zone drivers must observe the posted speed limits.

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.

Idaho bicycle stop-sign rule: A bicyclist approaching a stop sign may slow to a reasonable speed, yield when required, and proceed without a full stop when it is safe. At a steady red light, a bicyclist generally must stop and yield before proceeding as Idaho law allows.

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.
• When passing a bicyclist, Idaho Transportation Department guidance says to leave at least 3 feet of clearance and wait until road and traffic conditions allow a safe pass.
• 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.

Idaho slow-moving vehicle rule: A vehicle traveling slower than the normal speed of traffic and delaying three or more other vehicles in a rural area or on a two-lane highway must turn off the road wherever it is safe to let the other vehicles pass.

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

On undivided Idaho roads, traffic in both directions must stop for a school bus displaying flashing red lights while stopped to pick up or drop off children. Idahos four-lane exception: on highways with four or more lanes where two lanes travel in each direction, opposite-direction 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 a highway with two or more lanes of traffic traveling in each direction, oncoming traffic is not required to stop when meeting a stopped school bus.
• Traffic traveling in the same direction as the school bus must still stop; drivers traveling in the opposite direction should continue to watch carefully for children.
• 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: Idahos handbook warns that some buses and trucks are required to stop at all railroad crossings, so be prepared to stop if you are following one.

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 or police vehicle with lights flashing, or a tow truck or incident-response vehicle, 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 as soon as it is safe to do so.

8. DUI Laws & BAC Limits in Idaho

Idahos DUI law uses BAC thresholds of 0.08% for drivers age 21 or older, 0.02% for drivers under 21, and 0.04% while operating a commercial vehicle; a BAC of 0.20% or more carries enhanced penalties. Under Idahos implied-consent law, a first upheld refusal of a requested chemical test carries a one-year absolute license suspension and a $250 civil penalty.

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
• Within 20 feet of a fire station driveway
• In a designated bicycle lane
• 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

Idahos handbook emphasizes reducing speed, increasing following distance, and keeping windows and windshields clear when snow, ice, rain, fog, or other conditions reduce visibility or traction. In signed open-range areas, livestock are allowed to roam freely and have the right-of-way.

• 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.
• Studded snow tires: Idaho allows studded snow tires only from October 1 through April 30; ITD may adjust the dates in some years because of weather conditions.

12. Points & License Suspensions

Idahos point system uses 12-, 24-, and 36-month accumulation periods. Eight to 11 points in 12 months results in a warning letter; 12 to 17 points in 12 months brings a 30-day suspension, 18 to 23 points in 24 months brings a 90-day suspension, and 24 or more points in 36 months brings a 6-month suspension. Points may be removed once every three years through an approved course, subject to the programs rules.

Note: Points may be removed once every 3 years by completing either an ITD-approved Defensive Driving Course (DDC) or a qualifying Traffic Safety Education Course (TSC). A DDC can remove up to 3 points. A TSC offered by law enforcement at the time of a citation can remove up to 4 points and must be completed within 45 days of the citation. These courses remove points, not the conviction.

13. Headlight Rules

Idahos handbook sets firm headlight rules: headlamps and tail lamps must be lighted from sunset to sunrise and when poor visibility makes them necessary for safety. High beams must be dimmed 500 feet before meeting an oncoming vehicle and 200 feet before overtaking another vehicle.

Key test point: Idahos rule is 500 feet before meeting oncoming traffic and 200 feet before overtaking another vehicle. High beams must allow seeing people and vehicles at least 350 feet away; low beams must light the roadway at least 100 feet ahead.

14. Night Driving

At night, Idahos handbook advises drivers to reduce speed, avoid looking directly into oncoming headlights, keep the windshield and lights clean, and watch carefully for pedestrians, bicyclists, animals, and slow-moving vehicles that are harder to see in reduced visibility.

15. Cell Phones & Distracted Driving

Idahos hands-free law prohibits drivers from holding or supporting a mobile electronic device while driving. The rule applies to all drivers and continues to apply during brief stops at traffic signals and stop signs. Hands-free, one-touch, and voice-command functions are permitted within the law.

Key test point: Idaho is a hands-free state for all drivers. You may not hold or support a phone while driving, including while temporarily stopped at a traffic light or stop sign. To use a handheld device, the vehicle must be stationary and outside a public travel lane.

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 handbook covers roundabouts along with Thru-Turn intersections, Single Point Urban Interchanges (SPUIs), and Diverging Diamond Interchanges (DDIs). At a roundabout, entering drivers must yield to traffic already circulating in the circle.

Key rule: Yield to traffic already inside the roundabout, keep speed low, and turn on your right turn signal as you approach your exit.