This comprehensive guide to Idaho traffic laws provides clear, actionable explanations of the most commonly searched driving rules in the Gem State. Whether you're navigating I-84 through Boise, I-15 through Idaho Falls, mountain passes in Sun Valley, or rural highways in the Panhandle region, understanding Idaho-specific traffic regulations helps you stay safe and avoid costly violations. From double yellow line rules to mountain pass safety, wildlife crossing awareness, school bus stop requirements, speed limits, DUI regulations, and winter driving laws—every section references the official Idaho Code and guidance from the Idaho Transportation Department (ITD) and Idaho State Police. This is educational information, not legal advice; always obey posted signs, signals, and directions from law enforcement.
Idaho highways including I-84, I-15, US-95, and mountain passes require strict adherence to lane markings, wildlife awareness, and seasonal road conditions.
In Idaho, double solid yellow centerlines designate a no-passing zone where vehicles traveling in either direction are prohibited from crossing into the opposing lane to overtake another vehicle. According to Idaho Code § 49-630, these markings appear on curves, hills, narrow bridges, intersections, and areas where sight distance is limited. Violating this law can result in fines ranging from $100 to $300, plus 3 points on your Idaho driving record and potential insurance premium increases. Idaho State Police actively enforce no-passing zones on I-84, US-95, US-20, US-26, and mountain highways throughout the state including routes through Sun Valley, Stanley, and the Sawtooth Scenic Byway.
Legal Exceptions: When You May Cross Double Yellow Lines in Idaho
Idaho law recognizes several limited exceptions where drivers may legally cross double solid yellow lines:
Left turns into driveways and private roads: You may cross double yellow lines when making a left turn into a residential driveway, business entrance, ranch access road, forest service road, or private property entrance, provided it is safe and no oncoming traffic is present.
Avoiding obstructions: When a temporary obstruction blocks your lane—such as a disabled vehicle, fallen tree, rock slide debris, livestock, agricultural equipment, or road construction—you may briefly cross the centerline if the opposing lane is clear and the maneuver can be done safely.
Following official directions: When law enforcement officers, Idaho State Police, traffic control personnel, emergency responders, or construction flaggers direct you to cross the centerline, you must follow their instructions.
These exceptions do not permit passing slow-moving vehicles, farm equipment, logging trucks, or recreational vehicles in marked no-passing zones. The maneuver must be necessary, brief, and safe for all road users. Idaho's rural character means you'll frequently encounter slower traffic, but patience is legally required in no-passing zones marked with double yellow lines.
Mountain Highway No-Passing Zones: Safety in Steep Terrain
Idaho's mountain highways including US-95 north of McCall, ID-21 (Ponderosa Pine Scenic Byway), ID-75 (Sawtooth Scenic Byway), and US-20 through Island Park feature extensive double yellow line no-passing zones due to steep grades, sharp switchbacks, and limited sight distance. These scenic routes attract tourists, motorcyclists, and recreational vehicles, making illegal passing extremely dangerous. Idaho State Police conduct regular enforcement sweeps during summer tourist season (June-September). Mountain road violations often result in higher fines due to increased risk of head-on collisions on narrow roads with limited shoulders and steep drop-offs.
I-84 Corridor: Urban and Rural No-Passing Enforcement
Interstate 84 runs 275 miles across southern Idaho from the Oregon border through Boise to the Utah border. While I-84 is a divided highway with physical barriers and does not use double yellow centerlines for main travel lanes, entrance ramps, exit ramps, frontage roads, and connector roads frequently feature double yellow markings. Idaho State Police maintain high visibility on I-84 and issue citations for improper lane changes, unsafe passing on ramps, and violations on parallel surface streets. Always respect lane markings when entering or exiting the interstate.
Idaho law prohibits passing across double yellow lines but allows left turns into driveways and ranch roads when safe.
Idaho Right Turn on Red & Traffic Signal Laws
Idaho Code § 49-802: Right on Red After Complete Stop
Idaho law permits right turns on red signals after coming to a complete stop at the stop line, crosswalk, or intersection edge, unless a "NO TURN ON RED" sign prohibits it. Before turning, drivers must:
Come to a full stop—your vehicle must reach zero miles per hour
Yield to pedestrians in or approaching the crosswalk
Yield to all vehicles, bicycles, and motorcycles with the right-of-way
Check for "NO TURN ON RED" signs, which may apply at all times or during specific hours
Rolling through the stop or blocking the crosswalk is a common violation. Idaho courts treat incomplete stops seriously, with fines typically ranging from $90 to $165 plus court costs and 3 points on your license. In downtown Boise, Meridian, Idaho Falls, Pocatello, Coeur d'Alene, and Twin Falls, police closely monitor right-turn compliance at busy intersections.
Boise Downtown & University Areas: No Turn on Red Zones
Downtown Boise intersections near Capitol Boulevard, 8th Street, Grove Street, and the Boise State University campus frequently post "NO TURN ON RED" signs due to heavy pedestrian traffic, bike lanes, and complex signal phasing. Similarly, Idaho Falls intersections near downtown and Snake River Greenbelt crossings prohibit turns on red to protect pedestrian safety. Coeur d'Alene's Sherman Avenue and lakefront area also feature restricted intersections. Always read supplemental plaques beneath signs—some restrictions apply only during peak hours such as "NO TURN ON RED 7-9 AM / 3-6 PM MON-FRI."
Left Turn on Red in Idaho: One-Way to One-Way Streets
Idaho permits left turns on red from one-way streets onto other one-way streets, provided you come to a complete stop, yield to pedestrians and traffic, and no sign prohibits the turn. This scenario occurs primarily in downtown Boise's grid of one-way streets (including portions of Capitol Boulevard, Idaho Street, Main Street, and Front Street). Before attempting a left turn on red, verify that both streets are one-way in the appropriate directions and check for prohibitive signage.
Idaho Traffic Signal Timing & Yellow Light Duration Standards
Idaho traffic signals follow Idaho Transportation Department (ITD) and Federal Highway Administration (FHWA) guidelines for yellow (amber) light timing, typically 3-5 seconds depending on intersection speed limits and geometry. If you are already in the intersection when the light turns red, complete your movement safely. Entering on yellow is legal if you cannot stop safely; entering on red is a violation subject to citation.
Flashing Yellow Arrow Signals for Protected-Permissive Left Turns
Many Idaho intersections use flashing yellow arrow (FYA) signals for left turns. When you see a flashing yellow arrow, you may turn left after yielding to oncoming traffic and pedestrians—it functions like a traditional green ball for left turns but is more visible and intuitive. A solid yellow arrow means the protected phase is ending; stop if safe. A solid red arrow means you must stop and wait for a green arrow or flashing yellow arrow before turning.
Winter Traffic Signal Challenges: Snow Accumulation & Visibility
During Idaho's harsh winters, snow and ice can accumulate on traffic signal lenses, making colors difficult to distinguish. ITD maintains heated signal heads at critical intersections, but rural areas may experience temporary signal visibility issues. If you cannot clearly see signal colors due to snow buildup, treat the intersection as an all-way stop and proceed with extreme caution after yielding to all traffic. Report obscured signals to local authorities or ITD.
In Idaho, always stop fully and yield to pedestrians and cyclists before making a right turn on red.
Idaho School Bus Stop Laws & Strict Penalties
Idaho Code § 49-1422: Stopping for School Buses
Idaho enforces strict school bus stop laws to protect children. When a school bus activates flashing red lights and extends its stop arm, the following rules apply under Idaho Code § 49-1422:
Undivided roads (no median): All vehicles traveling in both directions must stop at least 20 feet from the bus and remain stopped until the red lights stop flashing and the stop arm retracts.
Divided highways (physical median or barrier): Only traffic traveling in the same direction as the bus must stop. Opposing traffic on the other side of a raised median, concrete barrier, or wide unpaved divider may proceed cautiously.
Multi-lane roads without median: All lanes in both directions must stop. Painted center turn lanes or double yellow lines do not count as physical dividers.
Passing a stopped school bus is a serious violation in Idaho. First-offense penalties include fines ranging from $100 to $500, 4 points on your license, possible license suspension for up to 30 days, and significantly increased insurance rates. Second and subsequent offenses carry mandatory license suspensions and increased fines up to $1,000.
Idaho School Bus Camera Programs: Stop-Arm Video Enforcement
Many Idaho school districts equip buses with exterior stop-arm cameras that record license plates of vehicles illegally passing stopped buses. Video footage is reviewed by local police or the Idaho State Police, who issue citations to registered owners. Camera-based enforcement has increased significantly in Boise, Meridian, Nampa, Idaho Falls, Pocatello, and other urban and suburban districts. Expect strict enforcement during morning (7-9 AM) and afternoon (2:30-4:30 PM) school hours on neighborhood streets and rural highways.
Flashing Yellow vs Flashing Red School Bus Signals in Idaho
Idaho school buses first activate flashing yellow lights approximately 100-300 feet before the intended stop to warn drivers that the bus is preparing to stop for children. You should slow down and prepare to stop but are not yet legally required to do so. Once the flashing red lightsactivate and the stop arm extends, you must come to a complete stop. Do not proceed until the red lights stop flashing, the stop arm retracts, and children are clear of the roadway. Bus drivers may signal you to proceed in some situations, but always wait for the lights and arm to retract.
Rural Highway School Bus Stops: Increased Danger & Strict Enforcement
Idaho's rural character means many school bus stops occur on highways with speed limits of 55-65 mph. Children crossing these high-speed roads face extreme danger from drivers who fail to stop. Idaho State Police conduct targeted enforcement operations on rural highways during school hours, especially on US-20, US-26, US-30, US-95, and state highways with known school bus routes. Fines for violations on rural highways may be enhanced due to the elevated risk to children.
On undivided Idaho roads, all traffic in both directions must stop when a school bus displays flashing red lights and extended stop arm.
Idaho's basic speed law requires drivers to operate at speeds reasonable and prudent for current road, traffic, and weather conditions. Even when traveling at or below the posted limit, you can be cited if your speed is unsafe for circumstances such as heavy rain, fog, snow, ice, wildlife crossings, or reduced visibility. Idaho Code § 49-654 also establishes statutory speed limits:
Residential and business districts: 25 mph (unless otherwise posted)
School zones: 20 mph when children are present or during posted hours
Interstate highways (I-84, I-15, I-86) for passenger vehicles: 80 mph on rural sections, 65 mph in urban areas
Trucks and vehicles towing trailers on interstates: 70 mph
Always adjust your speed for conditions. Posted limits represent the maximum safe speed under ideal dry-pavement, daylight, low-traffic conditions—not a target or minimum. Idaho's weather can change rapidly, especially in mountain areas where snow squalls, high winds, and black ice occur with little warning.
Idaho's interstate system includes I-84 (east-west across southern Idaho), I-15 (north-south through eastern Idaho), and I-86 (connecting Pocatello to I-84). Speed limits vary by section:
I-84 rural sections (Ontario, OR to Boise to Twin Falls to Utah): 80 mph for cars, 70 mph for trucks
I-84 Boise metro area: 65 mph
I-15 rural sections (Blackfoot to Idaho Falls to Pocatello to Utah/Montana borders): 80 mph for cars, 70 mph for trucks
I-15 Idaho Falls area: 65 mph
I-86 connecting Pocatello to American Falls: 75-80 mph
Idaho State Police conduct aggressive speed enforcement on interstates, especially during summer tourist season, holiday weekends, and high-traffic periods. Expect both stationary radar units and moving patrol enforcement. Speeding fines increase significantly for speeds exceeding 15 mph over the limit.
Idaho mountain passes including Fourth of July Pass (I-90), Lolo Pass (US-12), Teton Pass approaches, Galena Summit (ID-75), and Banner Summit (ID-21) feature reduced speed limits during winter months and adverse weather. When roads are snow-covered or icy, posted advisory speeds (yellow signs) indicate safe maximum speeds for current conditions. ITD also imposes traction tire requirements and chain requirements during severe winter weather. Violating chain requirements or driving too fast for winter conditions can result in citations, even if you're below the posted summer speed limit.
Idaho Point System & License Suspension Thresholds
Idaho uses a point system administered by the Idaho Transportation Department Driver Services. Speeding violations add points to your license:
1-15 mph over limit: 3 points
16+ mph over limit: 4 points
Reckless driving: 6 points
Accumulating 12-17 points in 12 months triggers a license suspension. 18-23 points results in a 90-day suspension; 24+ points results in a 1-year suspension. Drivers can attend a state-approved defensive driving course to reduce points by up to 3 points once every 36 months.
Work Zone Speed Limits & Enhanced Penalties
Idaho construction zones post reduced speed limits (typically 45-55 mph on highways, 25 mph in narrow work areas). When workers are present, Idaho law doubles fines for speeding and other moving violations. ITD posts "WORK ZONE / FINES DOUBLED WHEN WORKERS PRESENT" signs to remind drivers of enhanced penalties. A typical speeding ticket might cost $90; in an active work zone, the same violation could cost $180 plus court fees and points. Idaho's short construction season means intensive road work during summer months— expect frequent work zones May through October.
Idaho State Police use radar, LIDAR (laser), pacing, and occasional aircraft speed enforcement on rural interstates and highways. Radar detectors are legal for passenger vehicles in Idaho but do not exempt you from speed limits. Some rural interstate corridors use aircraft speed enforcement—watch for pavement markings and "SPEED ENFORCED BY AIRCRAFT" signs. Contesting speeding tickets requires appearing in the issuing magistrate court; consult a traffic attorney for serious violations that could result in license suspension.
Idaho DUI Laws & Driving Under the Influence Penalties
Idaho Code § 18-8004: Operating a Vehicle While Under the Influence
Idaho prohibits operating a motor vehicle with a blood alcohol concentration (BAC) of 0.08% or higher for drivers 21 and over, 0.02% or higher for drivers under 21 (zero tolerance for minors), and 0.04% or higher for commercial drivers. Even if your BAC is below the legal limit, you can still be charged with DUI if alcohol, drugs, or any intoxicating substance has impaired your ability to drive safely (Idaho Code § 18-8004). Idaho courts take DUI offenses seriously due to the state's rural character, long distances between communities, and high rate of single-vehicle crashes on remote highways.
First-Offense DUI Penalties in Idaho
A first-time DUI conviction in Idaho carries:
Fines: Up to $1,000 (often $1,000 plus court costs and fees)
Jail time: Up to 6 months (most first offenses result in 1-2 days jail with probation)
License suspension: 90-210 days (restricted permit may be available after 30 days)
Ignition interlock device requirement for license reinstatement (minimum 1 year)
Alcohol evaluation and mandatory substance abuse treatment if recommended
Community service hours as ordered by the court
Penalties increase substantially for repeat offenses, high BAC levels (0.20% or above), refusal to submit to chemical testing, or DUI incidents involving accidents, injuries, or minors in the vehicle. Idaho's "excessive DUI" charge applies to BAC of 0.20% or higher and carries enhanced minimum penalties.
Idaho Implied Consent Law & Chemical Test Refusal
Under Idaho's implied consent law (Idaho Code § 18-8002), by driving on Idaho roads you automatically consent to chemical testing (breath, blood, or urine) if lawfully arrested for DUI. Refusing the test results in automatic administrative license suspension:
First refusal: 1-year license suspension (no permit available)
Second refusal within 10 years: 2-year suspension
Third or subsequent refusal: Longer suspensions and enhanced DUI penalties if convicted
Refusal does not prevent prosecution—the state can still charge you with DUI based on officer observations, field sobriety tests, and other evidence. Refusal can be used against you in court and typically results in harsher penalties if convicted. You have the right to an administrative license suspension (ALS) hearing within 7 days of arrest to contest the suspension, but you must request it promptly.
Ignition Interlock Device Requirements in Idaho
Idaho law requires ignition interlock devices (IID) for all DUI offenders seeking license reinstatement or restricted driving privileges. An IID is a breath-testing device connected to your vehicle's ignition system. The engine will not start unless you provide a breath sample below the programmed limit (typically 0.02% BAC). Idaho requires IIDs for a minimum of 1 year for first offenders, 2 years for second offenders, and longer periods for repeat offenders. You must use a state-approved IID provider and pay all installation, monitoring, calibration, and removal costs (typically $75-$125/month). Attempting to circumvent the device or having someone else blow into it is a criminal offense that can result in additional jail time and extended license suspension.
Wildlife-Vehicle Collision Prevention on Idaho Highways
Idaho has substantial populations of deer, elk, moose, and other wildlife that frequently cross highways, particularly at dawn and dusk. Wildlife-vehicle collisions are a serious safety concern, especially on rural highways in eastern Idaho, the Panhandle region, and mountainous areas. Routes US-20, US-26, US-95, ID-21, ID-75, ID-55, and portions of I-15 and I-84 have high collision rates. Wildlife crossings peak during fall mating season (September-November) and spring migration (April-June), as well as during dawn (5-8 AM) and dusk (6-10 PM) hours year-round.
Recognizing Wildlife Crossing Warning Signs in Idaho
ITD places yellow diamond-shaped wildlife crossing warning signs in high-risk areas. These signs feature black silhouettes of deer, elk, or moose and indicate documented crossing zones. When you see these signs:
Reduce your speed, especially during dawn, dusk, and nighttime hours
Scan both roadsides constantly—animals blend into vegetation and are difficult to see
Use high-beam headlights when no oncoming traffic is present to spot eye reflection
Never swerve suddenly—brake firmly in a straight line if an animal appears
Watch for multiple animals—deer and elk often travel in groups
What to Do After a Wildlife Collision in Idaho
If you strike a deer, elk, or moose on an Idaho highway:
Pull safely off the roadway if possible and activate hazard lights
Call 911 or Idaho State Police to report the collision—especially if injuries or major damage occurred
Do not approach injured wildlife—a wounded elk or moose can be extremely dangerous
Contact your insurance company to file a claim (comprehensive coverage typically covers wildlife collisions)
Document the scene with photos for insurance purposes
Idaho law allows you to salvage roadkill meat if you obtain a free possession tag from the Idaho Department of Fish and Game within 72 hours of the collision. You can request a tag online or by calling Fish and Game.
Moose & Elk: Extreme Collision Danger on Mountain Highways
Moose and elk are significantly larger and more dangerous than deer in vehicle collisions. A full-grown moose can weigh 1,000-1,500 pounds; bull elk can exceed 700 pounds. When struck by a vehicle, their long legs collapse and their massive bodies crash through the windshield, often causing severe injuries or fatalities to vehicle occupants. Mountain highways in the Panhandle (US-95, US-2, ID-57), Sun Valley area (ID-75), Teton Valley (ID-33), and Island Park (US-20) have particularly high moose and elk populations. Drive with extreme caution in these areas, especially at night.
Idaho permits the use of studded tires from October 1 through April 30 each year without restriction. During this period, studded tires provide significantly improved traction on icy and snow-covered roads common throughout Idaho winters. Outside this period (May 1 through September 30), studded tires are prohibited unless road conditions warrant their use (snow, ice, or freezing conditions). Violating studded tire season restrictions can result in citations and fines.
Chain Requirements & Traction Tire Rules on Mountain Passes
ITD imposes traction tire or chain requirements on mountain passes and highways during winter storms. When "CHAINS REQUIRED" or "TRACTION TIRES REQUIRED" signs are posted, you must comply before proceeding. Traction tires include:
Studded snow tires with adequate tread depth (minimum 1/8 inch)
Winter tires with the three-peak mountain snowflake symbol and adequate tread
All-season tires with M+S (mud and snow) designation and adequate tread during some conditions
When "chains required" is posted, all vehicles (except those with four-wheel drive and adequate traction tires) must install chains on drive wheels. Commercial vehicles must carry chains at all times during winter months and install them when required. Violating chain requirements can result in citations, fines, and being turned back by law enforcement or ITD personnel at chain-up areas.
Idaho's mountain passes including Banner Summit (ID-21), Galena Summit (ID-75), Fourth of July Pass (I-90), Lolo Pass (US-12), and numerous sections of US-95 through the Panhandle experience temporary closures during severe winter storms. ITD monitors conditions and closes passes when avalanche danger is high, visibility is near zero, or road conditions become impassable. Always check ITD's 511 road conditions system before traveling on mountain highways during winter months. Attempting to bypass road closures is illegal and extremely dangerous.
Winter Driving Best Practices: Speed Reduction & Safe Following Distance
Idaho's basic speed law requires reducing speed for road and weather conditions. On snow-covered or icy roads, reduce speed by 10-20 mph below posted limits or more depending on conditions. Increase following distance to at least 8-10 seconds to allow for extended stopping distances on slippery surfaces. Avoid sudden braking, acceleration, or steering inputs that can cause loss of traction. If you begin to slide, ease off the gas and steer in the direction you want to go—do not brake hard or oversteer. Consider taking a winter driving course offered by Idaho State Police or private driving schools to improve your skills and confidence on winter roads.
This guide summarizes common Idaho traffic rules based on Idaho Code Title 49 and ITD guidance. It is not legal advice. Always follow posted signs, signals, and instructions from law enforcement. Consult an attorney for specific legal questions or if you are facing traffic citations or criminal charges.
