2005 California Vehicle Code Sections 41100-41104 CHAPTER 4. PRESUMPTIONS

41100.  In any action involving the question of unlawful speed of a
vehicle upon a highway which has been signposted with speed
restriction signs of a type complying with the requirements of this
code, it shall be presumed that existing facts authorize the erection
of the signs and that the prima facie speed limit on the highway is
the limit stated on the signs.  This presumption may be rebutted.
41101.  (a) Whenever a traffic sign or traffic control device is
placed in a position approximately conforming to the requirements of
this code, it shall be presumed to have been placed by the official
act or direction of lawful authority, unless the contrary is
established by competent evidence.
   (b) Any sign or traffic control device placed pursuant to this
code and purporting to conform to the lawful requirements pertaining
to it shall be presumed to comply with the requirements of this code
unless the contrary is established by competent evidence.
41104.  In any case, involving an accident or otherwise, where any
rear component of a train of vehicles fails to follow substantially
in the path of the towing vehicle while moving upon a highway, the
vehicle shall be presumed to have been operated in violation of
Section 21711.