21650.  Upon all highways, a vehicle shall be driven upon the right
half of the roadway, except as follows:
   (a) When overtaking and passing another vehicle proceeding in the
same direction under the rules governing that movement.
   (b) When placing a vehicle in a lawful position for, and when the
vehicle is lawfully making, a left turn.
   (c) When the right half of a roadway is closed to traffic under
construction or repair.
   (d) Upon a roadway restricted to one-way traffic.
   (e) When the roadway is not of sufficient width.
   (f) When the vehicle is necessarily traveling so slowly as to
impede the normal movement of traffic, that portion of the highway
adjacent to the right edge of the roadway may be utilized temporarily
when in a condition permitting safe operation.
   (g) This section does not prohibit the operation of bicycles on
any shoulder of a highway, where the operation is not otherwise
prohibited by this code or local ordinance.

21650.1.  A bicycle operated on a roadway, or the shoulder of a
highway, shall be operated in the same direction as vehicles are
required to be driven upon the roadway.