Colorado bans lane splitting but allows lane filtering under 15 mph

Colorado draws a line between splitting and filtering, and only the second one is legal. Splitting, meaning riding the seam between moving lanes, falls squarely under subsection (3)(a) and also under subsection (2), which bars a motorcycle or autocycle from overtaking or passing in the same lane occupied by the vehicle being overtaken. Filtering is the carve-out at subsection (3)(b)(I), and it opens with the words "Notwithstanding subsections (2) and (3)(a)", so it is a suspension of both prohibitions rather than a general permission.

All five conditions in (3)(b)(I) have to hold at the same moment. The vehicle being passed must be stopped. The vehicles in the adjacent lanes must also be stopped, if those lanes carry traffic in the same direction as the motorcycle. The road must have lanes wide enough to pass safely. The motorcycle must be travelling at fifteen miles per hour or less. And conditions must permit prudent operation while passing. Subsection (3)(b)(II) adds a stop rule with no grace period: once the vehicles being passed begin moving, the rider must cease filtering. In practice that turns a filtering move into something a rider completes at a red light or in a genuine stoppage on I-25 or I-70, not something used to work through slow-rolling traffic.

The exception is written for two-wheeled motorcycles only. An autocycle stays under the (3)(a) prohibition, and so does a three-wheeled motorcycle, even though C.R.S. § 42-1-102 (55) defines a motorcycle as a vehicle steered by handlebars, with a seat the rider sits astride, designed to travel on not more than three wheels. Subsection (3)(b)(III) then rules out three specific manoeuvres: passing on the right shoulder, passing to the right of a vehicle that is in the farthest right-hand lane where the highway is not limited access, and passing in a lane of traffic moving in the opposite direction. Nothing in the section authorises using the shoulder or a bike lane to get to the front of a queue.

The rest of the section still applies while filtering. Subsection (1) entitles every motorcycle to full use of a traffic lane and forbids any motor vehicle from being driven so as to deprive a motorcycle of that lane, except where motorcycles are riding two abreast. Subsection (4) caps riding at two abreast in a single lane. Subsection (5) disapplies subsections (2) and (3) to police officers performing official duties, so a Colorado State Patrol or Denver Police rider filtering to an incident is not committing an infraction.

The expiry dates matter to anyone relying on this. Subsection (3)(b)(IV) repeals the filtering exception effective September 1, 2027, so absent further legislation the flat prohibition returns on that date. Subsection (3)(c)(I) requires the Colorado Department of Transportation to analyse the safety effects and report to the General Assembly by January 1, 2027, covering motorcycle rear-end collisions before and after August 7, 2024, the severity of rear-end collisions in heavy traffic before and after that date, and side-swipe collisions while overtaking at under fifteen miles per hour. That reporting subsection itself repeals on July 1, 2028. Section 3 (2) of chapter 40, Session Laws of Colorado 2024, provides that the change applies to acts committed on or after August 7, 2024, so conduct before that date is judged under the old flat ban.

A violation of any provision of section 42-4-1503 is a class A traffic infraction under subsection (6). The penalty and surcharge schedule at C.R.S. § 42-4-1701 (4)(a)(I)(O), the block covering motorcycle violations, sets the figure for 42-4-1503 at a $30 penalty plus a $6 surcharge. Class A infractions run from a $15 minimum to a $100 maximum penalty under 42-4-1701 (3)(a)(I), and unlike class B infractions they do carry driver's licence points under 42-2-127, because the point bar in 42-4-1701 (3)(c) is limited to class B infractions.

A traffic infraction in Colorado is a civil matter under 42-4-1701 (1), decided by a county court judge or magistrate rather than prosecuted as a crime. The practical exposure from a filtering stop is usually larger than the fine: a rider who filters past traffic that has begun to move, or who uses the shoulder to reach the front, is outside subsection (3)(b) entirely and is back under the (3)(a) prohibition, and the same conduct in a collision hands the other driver a straightforward argument on fault. Motorcyclists remain subject to every other traffic rule while filtering, because C.R.S. § 42-4-1501 applies the traffic laws of article 4 to anyone operating a motorcycle.