California Code, Streets and Highways Code - SHC § 887.8

(a) After consulting with the law enforcement agency having primary traffic law enforcement responsibility with respect to the state highway, the department may construct and maintain nonmotorized transportation facilities approximately paralleling that highway.

(b) Where the traffic safety or capacity of the highway would be increased, the department shall pay for the construction and maintenance of nonmotorized transportation facilities approximately paralleling the highway.

(c) The Legislature finds and declares that the construction and maintenance of nonmotorized transportation facilities constitute a highway purpose under Article XIX of the California Constitution, and justify the expenditure of highway funds and the exercise of the power of eminent domain therefor.