California Code, Streets and Highways Code - SHC § 30158

The department may issue permits for the use of any toll bridge or other toll highway crossing acquired or constructed pursuant to this chapter on a credit basis.  Except in the case of municipal or other public corporations, governmental agencies, or common carriers having contracts directly with the commission for the operation of the transportation facilities of the bridge or crossing, and except as provided in Section 30161.5, the department shall require the holder of a permit for the use of any toll bridge or other toll highway crossing on a credit basis to furnish and maintain in force a bond executed by an admitted surety insurer, approved by the department, in an amount equal to twice the department's estimate of the toll charges to be incurred under the permit during one month.