California Code, Streets and Highways Code - SHC § 254

As specific locations are determined by the commission for portions of state highways included in the California freeway and expressway system, the commission shall designate the particular portion as a part of the California freeway and expressway system and the planning and design of such highways shall include provision for such access control as the department and the commission determine essential to protect the investment of any improvements made and to permit the ultimate development of a full freeway or an expressway when traffic and other conditions require.  Such declaration by the commission shall have the effect of declaring the particular portion affected a freeway within the meaning of Section 100.2.