(KTLA/NEXSTAR) – If you’ve ever been startled out of the doldrums of your afternoon commute by a thundering, lane-splitting Harley Davidson and cursed whoever is responsible, you’re not alone.

You would also be correct in thinking that the biker just committed a traffic violation — unless you live in California.

Before you blast the California Highway Patrol with emails listing all the reasons why that congestion-cutting biker should be given a ticket and told to stay in his lane, the CHP has some information to share.

First, not only is lane-sharing or lane-splitting legal in California, but the CHP wrote the safety guidelines as instructed in AB51, which was approved by Gov. Jerry Brown in 2016.

Lane-sharing occurs in other states, of course, although California is the only place where the practice has been made legal. But why?

Well, one reason is that lane-sharing has been going on in California ever since motorcycles have been on the freeway, so it was important to set some ground rules, CHP Motorcycle Officer Brian O’Toole said. The second, and maybe more interesting reason, is that it makes time spent on the freeway shorter, not only for motorcyclists but for four-wheel motorists as well.

“As motorcycles are moving through, splitting the lanes … that’s one less vehicle occupying that lane,” CHP Motorcycle Officer Brian O’Toole said.

“It’s saving the average motorist in a car time,” he added. “If we were to … not allow lane-splitting anymore, that’s a motorcycle sitting in the lane ahead of them,” O’Toole said.

But just because the motorcyclist has the CHP on their side when it comes to lane-sharing, it doesn’t mean they can recklessly speed past you.

“It’s still a privilege,” O’Toole said. “We’re the only state left, so it’s a privilege for us to do this.”

California’s guidelines say bikers should only split lanes when the flow of traffic is 40 mph or less, and not travel more than 10 mph faster than the vehicles surrounding them. It’s also always up to an officer’s discretion as to whether the motorcyclist’s actions are deemed unsafe.

California’s four-wheeled motorists can help out too, according to O’Toole, by moving to one side of the lane to create a “gap” for motorcyclists to pass. “It’s a win-win situation for both,” he said.

Drivers throughout the country, however, are likely familiar with the concept of lane-splitting — whether it’s legal or not. In fact, Utah is the only state aside from California that has legalized any kind of lane-sharing, though Utah’s law applies only under very specific circumstances. Specifically, a motorcyclist in Utah may move between lanes of stopped traffic to the front, and typically only at an intersection, to reduce occurrences of rear-end collisions by approaching vehicles. The practice, known as “lane-filtering,” was made legal in 2019.

Legislative officials in several other states have proposed similar laws, though none have been formally adopted. Many proponents also point to a 2015 study conducted by U.C. Berkeley that suggests lane-splitting does not increase the risk of injury to motorcyclists who are traveling less than 15 mph faster than the surrounding traffic, if that traffic is going no faster than 50 mph. California’s law, as stated earlier, only allows lane-splitting when traffic is moving at 40 mph or less, and prohibits bikers from going over 10 mph faster than the traffic.

“It’s important to note that from the data in our study, we are unable to estimate the risk of getting into a collision in the first place,” said lead author Thomas Rice. “What we can do is look at motorcycle collisions that have occurred, and determine whether lane-splitting poses a greater risk of injury to riders, and whether the manner in which riders were lane-splitting was predictive of particular injury types.”