This article is from the California Driving (and Surviving) FAQ, by "George J Wu" email@example.com with numerous contributions by others.
from firstname.lastname@example.org (Sidney Markowitz) on 21 Jun 1993,
modified on 23 Jun after further research:
The motorcycle drivers handbook handed out by the DMV discourages lane
sharing (driving alongside cars in the same lane) because it is often a
violation of the Basic Speed Law (CVC 22350) or involves unsafe lane
changes. However, that statement in itself indicates that there is no law
against lane sharing, and that a rider can be cited only if the act violates
one of the other laws.
Many states other than California explicitly make lane sharing illegal.
California does make "lane splitting", occupying two lanes by riding the
line between them, illegal, I believe in CVC 21658(a):
A vehicle shall be driven as nearly as practical entirely within
a single lane and shall not be moved from the lane until such
movement can be made with reasonable safety.
The common response that I got from a query to ba.motorcycles on this
subject is that Bay Area cops do not ticket for riding a motorcycle slowly
(on the order of 10mph faster than the cars) alongside a line of cars
stopped at a traffic light or stuck in a traffic jam, as long as you are
within a lane (not on the shoulder). However, it also seems common
net.wisdom that police in Marin County and in Fremont do issue tickets for
that behavior. The important point is that the tickets are for violation of
the basic speed law or for unsafe lane changes, which are subject to the
judgement of the officer and so are pretty difficult to challenge in court.
Regardless of the warnings in the DMV handbook, I and many other people have
been taught in the Motorcycle Safety Foundation's rider training course that
it may be safer for motorcyclists to slowly and carefully ride alongside a
line of stopped cars than to sit in line where they may be rearended by a
car that is not paying attention. Also, many motorcycles are air cooled and
will overheat in just a few minutes of idling while sitting still.
This is one of my major peeves: That so many motorists act like I'm doing
something illegal and unfair by riding where they can't drive when I lane
share at a light, and that there is absolutely no mention of the motorcycle
laws on the standard driver's license exam, so there is no reason for them
to know better.
There: Now a few more car drivers know about this. When you see a
motorcyclist riding by you when you are stopped or almost stopped, don't
swerve out to cut them off. They are legal (if they are being careful),
they may be acting out of safety considerations, and they are reducing
traffic congestion by getting out of the thick of it instead of being part