Idaho Has No Lane-Splitting Law: the Single-Lane Duty Governs

Idaho's motorcycle sections are easy to enumerate because there are so few of them. Chapter 6 of title 49, the rules of the road, contains section 49-665 on riding on motorcycles, which addresses only the seat and passengers, and section 49-666 on helmets and seatbelts for riders under 18. There is no section 49-664. The lane-position section that most western states carry, the one that says a motorcycle is entitled to the full use of a lane and that no motorcycle shall be operated between lanes or between adjacent rows of vehicles, was never enacted here. Idaho also has no two-abreast lane-sharing provision for motorcycles: the only riding-two-abreast section in title 49 is section 49-718, and it is about bicycles.

That absence has a consequence riders sometimes get backwards. Because there is no authorising section, filtering forward between stopped cars at a Boise or Coeur d'Alene traffic light is not permitted by silence. It falls under section 49-637, which applies whenever a highway has been divided into two or more clearly marked lanes and requires in subsection (1) that a vehicle be driven as nearly as practicable entirely within a single lane and not moved from that lane until the driver has first ascertained that the movement can be made with safety. A motorcycle is a vehicle for these purposes, and riding along the paint line between two lanes of traffic is not driving as nearly as practicable within a single lane.

The overtaking rules close the other route. Section 49-633(1) allows a driver to overtake and pass on the right only when the vehicle overtaken is making or about to make a left turn, or upon a highway with unobstructed pavement of sufficient width for two or more lines of vehicles moving lawfully in the direction being travelled. Subsection (2) adds that passing on the right may be done only under conditions permitting the movement in safety, and that it shall not be made by driving off the roadway. Section 49-632(1) requires an overtaking vehicle to pass to the left at a safe distance and not return to the right until safely clear. None of that authorises threading a gap that is not itself a lawful line of travel.

Idaho does give motorcycles two real privileges that riders should not confuse with filtering. Section 49-1421A(2) allows a person to drive a motorcycle in a high occupancy vehicle lane at any time regardless of the number of passengers and without penalty, while a car with fewer than two occupants in a restricted HOV lane commits an infraction with a fixed penalty of one hundred dollars under subsection (6). And section 49-654(1)(b) lets the driver of a passenger car, motorcycle or pickup truck not towing anything exceed the posted limit by up to fifteen miles per hour while passing a slower vehicle, but only when passing on the left on a two-lane road posted at 55 miles per hour or more, or when passing in a designated passing lane. That allowance does not apply within an incorporated city, in construction zones, on roads posted below 55, or to passing on the right within a passing-lane area.

One further Idaho provision shapes how this plays out at the roadside. Idaho Code section 49-1431, added in 2020, prohibits any state or local law enforcement agent or agency from engaging in motorcycle profiling, defined as the arbitrary use of the fact that a person rides a motorcycle or wears motorcycle-related paraphernalia as a factor in deciding to stop, question, take enforcement action against, arrest or search a person or vehicle. Subsection (3) is equally important: the section expressly does not create a cause of action against any individual, the state, any county or city, or any law enforcement entity. It is a standard of conduct, not a remedy a cited rider can sue on.

A lane-position violation is charged under Idaho Code section 49-637, which sits in chapter 6 of title 49. Idaho Code section 49-236(2) makes any violation of chapters 3, 4 and 6 through 9 of title 49 an infraction unless otherwise specified, so failing to keep within a single lane carries no jail and no criminal record. 50 before the statutory court costs, surcharges and fees are added. Enforcement is by Idaho State Police on state highways and interstates and by city police and county sheriffs elsewhere; there is no camera enforcement route, because section 49-1432(2)(b) bars an agency from using automated license plate reader data to enforce traffic infractions other than those associated with a traffic accident.

The more serious exposure from a split-lane collision is civil rather than criminal: a rider found to have been outside the single-lane rule when a driver changed lanes into him will face a comparative-fault argument built directly on section 49-637(1). Contest a citation in the magistrate division of the district court for the county where it issued; Rule 9 forbids a withheld judgment or a suspended penalty on an infraction.