The code section that the Branciforte protestors were allegedly violating was "section 21350". I'm not sure but I believe they were referring to the CA vehicle code.

I agree that Cal-Trans may not have jurisdiction. The freeway overpasses could be like condominiums in that the community property begins at the outside wall of the condo, but the interior is the private property of the tennant. Simillarly, I am willing to bet that Cal-Trans has jurisdiction over the traffic signs mounted on the outsides of the overpasses, but does not have control over what happens on the public sidewalks that are part of the interior of the overpasses.