This August, Coloradans waiting at stoplights may be shocked to see motorcycles passing their cars. But Colorado just became the third state to officially allow the practice–known as lane filtering or “filtering up.” Why did Colorado decide filtering is fine? Its an effort to make roads safer.

In 2023, 134 motorcyclists were killed on Colorado roads. State Patrol trooper Gabriel Moltrer said, “Colorado’s new lane filtering law could save motorcyclists from injuries or death…Lane filtering reduces the chance of motorcyclists being rear-ended by a car or truck in high-volume, stop-and-go traffic. Collisions from behind by larger vehicles can cause serious injury or kill motorcycle riders.”

Colorado Senate Bill 24-0749 allows motorcycles to pass stopped vehicles which are traveling in the same direction. They are supposed to pass said vehicles on the left, but not enter the oncoming traffic lane–even if it is empty. It will be most useful at traffic lights and in gridlocked traffic. This can get motorcyclists out of that “vulnerable” position of being trapped in the middle of stop-and-go traffic.

Another benefit of “filtering up” is to improve the flow of traffic. The logic is that motorcycles will accelerate away from stoplights quicker than most trucks and cars. So if they filter up to the front of the line, they’ll accelerate toward the next clump of traffic, effectively spreading out the vehicles on the road and reducing congestion.

Finally, lane filtering just makes motorcycling more convenient by reducing travel times for motorcyclists in downtown areas. At the same time, it doesn’t really affect other motorists.

Filtering is not to be confused with lane splitting. The latter includes riding down the line dividing two lanes of slow-moving traffic. Colorado State Patrol Chief Col. Matthew Packard said, “The first thing Coloradans need to understand is that there is a seemingly small but important difference between lane filtering and lane splitting…One will soon be legal, and the other remains prohibited, so let’s all start by getting on the same page.” In fact, the CSP urges motorists to call *277 and report lane splitting.

Lane filtering is legal in Utah, and California (in the latter state, lane splitting is also legal). Hawaii specifies that “shoulder surfing” is legal. That’s the most Hawaiian name ever. But it just means that motorcycles can pass stopped traffic on the shoulder, but not by passing between lanes. On August 7th, Colorado will become the third state to expressly allow lane filtering.

Note that only 29 states have laws prohibiting lane filtering. Twelve states not only don’t prohibit it, they have no law on the books to define it. In these states, you could say that lane filtering isn’t technically illegal. But obviously, a police officer can always pull over a motorcyclist for riding dangerously if they see them lane splitting or filtering.

Next, see our list of every states lane filtering and splitting laws, or learn about lane splitting from the motorcyclist’s perspective in the video below: