In California:<p>CVC 21654:<p>(a) <i>Notwithstanding the prima facie speed limits</i>, any
vehicle proceeding upon a highway at a speed less than the normal
speed of traffic moving in the same direction at such time shall be
driven in the right-hand lane for traffic or as close as practicable
to the right-hand edge or curb, except when overtaking and passing
another vehicle proceeding in the same direction or when preparing
for a left turn at an intersection or into a private road or
driveway.<p>(b) If a vehicle is being driven at a speed less than the normal
speed of traffic moving in the same direction at such time, and is
not being driven in the right-hand lane for traffic or as close as
practicable to the right-hand edge or curb, it shall constitute prima
facie evidence that the driver is operating the vehicle in violation
of subdivision (a) of this section.<p>(AKA &quot;Slower traffic, keep right&quot; law)