Cal. Sts. & Hy. Code § 5101.7
The legislative body of a city may order the construction and installation of improvements authorized by Section 5101 in the right-of-way of a state highway or county road, or in a railroad right-of-way which is located within or adjacent to the corporate boundaries of the city, or in the right-of-way of a county road which is or will be an extension of a street, public way, or right-of-way of the city, if the legislative body determines that the public interest or convenience requires the construction and installation and that the land within an assessment district to be assessed to pay the cost and expenses of the improvements is benefited thereby. The construction and installation of the improvements in the right-of-way may be performed pursuant to a permit, license, lease, easement, or right-of-way granted to the city by the public entity or corporation having jursidiction and control over the highway, road, or right-of-way. The legislative body of the city may establish and change the grades of the highway, road, or right-of-way, or portion thereof, where the improvement will be constructed in cooperation with the public entity or corporation having jurisdiction and control over the highway, road, or right-of-way. Before ordering the construction and installation of the improvements, the city shall obtain the approval of the public entity or corporation having jurisdiction and control over the highway, road, or right-of-way. Notwithstanding the provisions of this section, the legislative body shall not order the construction or improvement of a segment of a state highway except as provided in Section 5101.8.
Ca. Sts. and High. Code § 5101.7