21208.  (a) Whenever a bicycle lane has been established on a
roadway pursuant to Section 21207, any person operating a bicycle
upon the roadway at a speed less than the normal speed of traffic
moving in the same direction at that time shall ride within the
bicycle lane, except that the person may move out of the lane under
any of the following situations:
   (1) When overtaking and passing another bicycle, vehicle, or
pedestrian within the lane or about to enter the lane if the
overtaking and passing cannot be done safely within the lane.
   (2) When preparing for a left turn at an intersection or into a
private road or driveway.
   (3) When reasonably necessary to leave the bicycle lane to avoid
debris or other hazardous conditions.
   (4) When approaching a place where a right turn is authorized.
   (b) No person operating a bicycle shall leave a bicycle lane until
the movement can be made with reasonable safety and then only after
giving an appropriate signal in the manner provided in Chapter 6
(commencing with Section 22100) in the event that any vehicle may be
affected by the movement.