Colorado’s lane-filtering law for motorcyclists has been in effect for more than a year, but it’s still too soon to know if it has helped prevent motorcycle crashes and injuries, as the law was intended to do.

The new law allows motorcyclists to pass stopped vehicles while going 15 mph or less, if the lane is wide enough for them to pass safely on the left of the stopped vehicle while staying in the same traffic lane as the overtaken car – and without entering the oncoming lane or on the right shoulder.

Riding between lanes of stopped traffic on the lane marker line is not permitted, even if all traffic is stopped.

“The purpose of the law was to try to reduce car accidents,” said Jerry Bowman of Bowman Law of Denver, which has specialized in Colorado motorcycle law for more than 13 years. “The idea being that a motorcyclist is kind of in a vulnerable position behind a vehicle and an approaching vehicle, whether they’re paying attention or not. Sometimes, there’s these incidences when they don’t have time to stop and when there’s a motorcyclist there, that’s an issue. So, allowing filtering allows the rider to move out of that area.”

The law could potentially lower the number of motorcyclist deaths in Colorado, he said.

But a lot of motorcycle riders are still unclear about the difference between lane filtering, and lane splitting — which is still not legal here.

Going into effect Aug. 7, 2024, the lane-filtering law differs from California’s lane-splitting law, which allows motorcyclists to navigate between moving lanes of traffic at higher speeds. Colorado’s version limits the practice to congestion or stoplights, aiming to reduce rear-end collision risks without encouraging aggressive maneuvering.

Proponents of lane filtering have cited California studies for support. A 2015 UC Berkeley report on nearly 6,000 crashes found that lane-splitting riders were 43% less likely to be rear-ended and had lower injury severity when the speed difference was under 15 mph. Another study on CHP safety guidelines showed a 30% drop in fatalities.

Critics, including some law enforcement officials, expressed worries about driver confusion or the risk of side-swipes.

Colorado became the fifth state to legalize lane filtering for motorcycles under Senate Bill 24-079.

“There’s often liability disputes when we’re talking about a motorcyclist who filters a lane or who tries to split a lane, for instance,” Bowman said. “The question is, who is ultimately responsible?”

The chief of the Colorado State Patrol said the blame for a crash falls on the motorcycle rider — if the cars are moving, however slowly.

“Based on our law, if vehicles are moving, even slowly or for a short distance, the motorcyclist would be at fault,” said Col. Matthew Packard, the head of the Colorado State Patrol. “Riders are responsible for ensuring that all conditions are met to safely and legally filter.”

He noted that the law specifically states that, in order to pass, traffic in the same direction as the motorcycle rider must be stopped entirely. Here are the specifications from the Colorado State Patrol:

•To pass, traffic in the rider’s lane and adjacent lanes going the same direction must be at a complete stop.

•The lane must be wide enough to fit the vehicle and motorcycle while passing

•The motorcycle must go 15 mph or less

•The rider must pass safely and control the motorcycle

•The rider must pass on the left and not enter the oncoming traffic lane

Bowman said a big part of the problem is that “not all motorcyclists understand the law” and the difference between splitting and filtering.

“Motorcycle accidents can be more severe, more likely when riders attempt to maneuver something too fast, when they try to do lane splitting, as opposed to lane filtering with moving traffic, or when drivers do not really expect it,” he said.

Supporters hope the new law would decrease rear-end collisions of motorcyclists, crashes that typically result in serious bodily injury or death.

The law requires the Colorado Department of Transportation to collect data on the safety and effectiveness of the new law and report to the Colorado General Assembly in 2027.

Dennis Huspeni and Abbey Soukup contributed to this article.