California Code, Vehicle Code - VEH § 34020.5

(a) The Department of Transportation, after consultation with the Department of the California Highway Patrol, the State Fire Marshal, and affected local agencies, and following a public hearing subject to Section 21109.5, may regulate the time when tank vehicles may travel through a tunnel on state highways.

(b) In evaluating the use of a tunnel on a state highway, the Department of Transportation shall conduct a traffic and engineering survey which includes an analysis of the relative risks to public safety in determining the feasibility of reasonable alternative routes.

(c) For the purposes of this section, a tunnel is a horizontal passage enclosed on the sides and top containing a roadway of a length of not less than 300 feet.

(d) No prohibition or restriction adopted pursuant to this section shall be effective until appropriate signs have been posted giving notice thereof to drivers approaching the tunnel.