lane-splitting is lane-sharing

This is still in quite rough form. Bear with me as I elaborate. The premise is (motorcycle) lane-splitting is related to (bicycle) lane sharing.

Lane splitting Legal Misconception

Note that the motorcyclist is NOT driving on the lane line

I was under the impression, what I believe now to be a common misconception, that motorcycle lane-splitting refers to a motorcyclists splitting between two lanes; in other words riding on the dashed line.

There are two related traffic rules, the first is general and applies to all persons driving any vehicle: motorcyclists, motorists driving cars/trucks, and incidentally also to bicyclists. This general rule implicitly makes lane-splitting by riding on the dashed line illegal.
The second law explicitly makes any form of motorcyclist lane-splitting illegal; both riding on the dashed line (section C) or riding within the same lane regardless of the lane’s width (section B).

§28-729. Driving on roadways laned for traffic
If a roadway is divided into two or more clearly marked lanes for traffic, the following rules in addition to all others consistent with this section apply:
1. A person shall drive a vehicle as nearly as practicable entirely within a single lane and shall not move the vehicle from that lane until the driver has first ascertained that the movement can be made with safety.

 §28-903.  Operation of motorcycle on laned roadway; exceptions
A. All motorcycles are entitled to the full use of a lane. A person shall not drive a motor vehicle in such a manner as to deprive any motorcycle of the full use of a lane. This subsection does not apply to motorcycles operated two abreast in a single lane.
B. The operator of a motorcycle shall not overtake and pass in the same lane occupied by the vehicle being overtaken.
C. A person shall not operate a motorcycle between the lanes of traffic or between adjacent rows of vehicles…

It actually technically refers to splitting the space in one lane among a motorcycle and another vehicle. This is explicitly illegal in AZ (as mentioned above, 28-903B) and apparently all other states except CA because (see e.g. the picture of the “sign” above and info at ).

NOTE WELL!! Except for the motorcycle exception (28-903A);  Two vehicles may share lanes. What? This is confusing to a lot of people. The simple answer is 1) there is no law against it, and 2) the vast majority of lanes are nowhere near wide enough to comfortably allow two cars to fit side-by-side.

Still not-illegal in CA: AB51

The situation in CA is quite intriguing:  as explained by, the situation in CA is that lane-splitting (as in lane-sharing) is not illegal, in other words, CA law lacks a provision like Arizona’s 28-903B or C.

Things got heated when in 2013 CHP published “guidelines” for how to lane split — implying it was legal to split.  Under pressure from an anti-splitter group (who knew?) CHP “quietly removed”  the guidelines in 2014. Which of course didn’t actually change anything.

Ultimately, AB51 passed in 2016; and while often referred to as legalizing lane-splitting, that’s not exactly true. No rules of the road were changed; the law simple empowers CHP (and some others) to develop and publish guidelines via a new section VC 21658.1. And in fact, 21658 is still the law of the land; it is CA’s equivalent to 28-729.1, “A vehicle shall be driven as nearly as practical entirely within a single lane…”.

Example of motorcyclists legally sharing/”splitting” a lane in CA (not straddling lanes).

Arizona Legislation

A New Times article on the subject refers to a 2010 that was vetoed; and in any event there are now two versions floating around in the Spring 2018 legislative session:

  • SB1007 As simply eliminated 28-903B & C and adds “guideline” language similar to CA’s law. It does not touch 28-723.
  • SB1015 waives 903B & C for helmeted motorcyclists, and sets some mph limits.

Ug. helmet debate. AZ has no adult helmet law.


Bicyclists Lane-sharing

The whole situation for bicyclists is like some sort of bizzaro world version of motorcyclist lane-splitting.

Motorcyclists split in order to get ahead of slower traffic.

Motorists lane-split bicyclists in order to get ahead of slower bicyclists.

FTR laws in effect force bicyclists to allow motorists to lane-split them; the safety exceptions are unknown to or routinely ignored (by motorists who get agitated at any bicyclist not riding FTR)

i have many more thoughts about this; free-association — the same people who insist motorcyclist lane-splitting is horribly dangerous i suspect are the same ones who think controlling a narrow lane (on a bicycle) is horribly dangerous (they also think it’s already illegal). They are all for forced lane-splitting when it’s them wanting to pass a bicyclist within a lane, at infinite mph speed differential.

The Berkely (motorcyclist) lane-splitting study 2015 generally found motorcycle lane-splitting to be acceptably safe. Because, or at least in part because the demographic (more full-face helmets) and speeds of lane-splitters (a majority are < 15mph differential).


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