Motorcycle Lane Filtering in Colorado – What You Need to Know

Colorado Senate Bill 24-079 went into effect on August 7, 2024, allowing motorcyclists to filter between stopped cars on the roadway, also known as lane filtering. 

The Colorado State Patrol (CSP) defines lane filtering as: “The act of a rider passing a vehicle in the same lane but only when that vehicle and any traffic in adjacent lanes are at a complete stop. This maneuver will likely be most common at stop lights or gridlocked traffic and will legally allow riders to navigate toward the front of the line, avoiding being sandwiched between two vehicles.” [1] 

Colorado is the fifth state to allow lane filtering, joining California, Utah, Montana and Arizona [2]. The bill permits motorcyclists to pass other vehicles in the same lane if certain conditions are met [3]:

• The overtaken or passed vehicle is stopped.
• The vehicles in the adjacent lanes are stopped.
• The operator of the motorcycle is on a road with lanes wide enough to pass safely.
• The passing motorcycle is driving at fifteen miles per hour or less.
• Conditions permit prudent operation of the motorcycle while passing.

The bill further clarifies that once the vehicles that are being passed begin to move, the motorcyclist must stop filtering. Additionally, the bill states that motorcyclists may not pass on the right shoulder, may not pass to the right of a vehicle in the farthest right lane if the highway is not limited access, and may not pass in a lane of traffic moving in the opposite direction [3].

The law is set to automatically expire in September 2027. As part of the law, the Colorado Department of Transportation (CDOT) will be collecting data on motorcycle sideswipe and rear-end crashes during the next three years to compare with data from before the law’s effective date [1, 3]. Their findings will be considered by the Colorado legislature in determining if any action should be taken, such as extending or modifying the law.

CSP stated that while lane filtering is legal as of August 7, lane splitting is not [1]. The primary differences between lane filtering and lane splitting are outlined below: 

• Lane filtering occurs only when surrounding traffic is stopped. An example of lane filtering is when a motorcyclist passes between stopped vehicles lined up at a red traffic light, proceeding to the front of the line. This type of maneuver is legal in Colorado as of August 7. 
• Lane splitting involves motorcycles passing between lanes of moving traffic. An example of lane splitting is when a motorcyclist passes between two moving vehicles while riding on a freeway or interstate. This type of maneuver is NOT legal in Colorado under the new law.

Lane Filtering and Splitting Laws in Other States

Other states who have legalized lane filtering recently include Utah, Montana, and Arizona. The Utah law, which went into effect in 2019, permits lane filtering between stopped traffic anywhere the speed limit is 45 miles per hour or less, if the roadway has two or more lanes in the same direction of travel, and the motorcyclist travels at 15 miles per hour or less. It specifies that motorcyclists cannot lane filter on shoulders or bike lanes and that motorcyclists must merge back into a lane as soon as possible once traffic begins moving [5].

In Montana, lane filtering became legal in 2021. The law specifies that a motorcyclist can lane filter when the roadway has lanes wide enough to pass safely and the motorcycle is traveling at 20 miles per hour or less. Montana defines lane filtering as “the act of overtaking and passing another vehicle that is stopped or traveling at a speed not in excess of 10 miles an hour in the same direction of travel and in the same lane.” [6]

The Arizona law, which went into effect in 2022, allows motorcyclists to pass between stopped vehicles if the street has at least two lanes of traffic in the same direction the motorcyclist is traveling, if the road has a speed limit of 45 miles per hour or less, and if the motorcyclist travels at 15 miles per hour or less while lane filtering [7].

Lane splitting and lane filtering are both legal in California, which defines lane splitting as: “Driving a motorcycle that has two wheels in contact with the ground, between rows of stopped or moving vehicles in the same lane, including on both divided and undivided streets, roads, or highways.” [8] The California Highway Patrol developed a list of safety tips to assist motorcyclists while lane splitting. The list stated that danger increases as speed increases and as the speed differential between the motorcyclist and surrounding traffic increases. The list also says that it is typically safer to split between the far-left lanes of a roadway than between other lanes and that riding on the shoulder is not considered lane splitting and is illegal [9].

( For more information on lane filtering and lane splitting in California, see the article titled “Motorcycle Accident Reconstruction: Lane-Splitting, Lane-Sharing, and Filtering in California” from Explico’s Principal Accident Reconstructionist, Nathan Rose.)

In addition to the above states, Minnesota will permit lane filtering and lane splitting beginning on July 1, 2025. The Minnesota law will allow motorcyclists to pass between lanes of traffic traveling in the same direction if the motorcyclist is traveling 40 miles per hour or less and as long as the motorcyclist does not travel more than 15 miles per hour faster than surrounding traffic. The Minnesota law also indicates that motorists who try to prevent motorcyclists from legally lane splitting may be charged with a misdemeanor [10].

The Data Behind Lane Filtering and Splitting

Many of the laws mentioned in this article reference a 2015 study by the Safe Transportation Research and Education Center at the University of California Berkeley [10]. The study looked into data from the California Enhanced Motorcycle Collision Data Project, which contained 5,969 motorcycle crashes between June 2012 and August 2013, in order to determine how common lane splitting-related collisions were and how likely different types of injury were. The study found 997 lane splitting collisions and found that lane splitting motorcyclists were less likely to be injured. A key finding of the study was that traffic speed and the speed differential between the motorcycle speed and traffic speed were related to injury likelihood. The authors reported that at speed differentials greater than 15 miles per hour, increased speed differential resulted in increased risk of injury. Similarly, lane splitting with a traffic speed of greater than 50 miles per hour resulted in an increased risk of injury. Lane splitting motorcyclists were less likely to be rear-ended [11].

Lane filtering is a controversial issue, but according to the results of the Berkeley study, it does reduce the likelihood of motorcyclists being struck from behind in stopped or slow-moving traffic. According to the state of Utah, lane filtering decreases congestion at busy traffic signals and helps to reduce the likelihood of a motorcyclist being rear-ended at a red light [5]. Lane filtering also helps to prevent air-cooled motorcycles from overheating and breaking down on the road. Many modern cruiser-style bikes are still air-cooled and rely on airflow from the motorcycle’s movement to keep the engine cool.

In the unfortunate situation that a lane-filtering or lane-splitting crash occurs, Explico can evaluate the actions of the motorcyclist and other involved drivers to help determine what happened and how the crash could have been avoided.