The department may transfer or loan, or both, funds between the Toll Bridge Seismic Retrofit Account in the State Transportation Fund and the State Highway Account for cash flow purposes to accomplish individual toll bridge seismic requirements. No funds may be transferred or loaned from the State Highway Account to fund any amenity, as defined by Section 31000, or to fund shortages that result from the expenditure of funds from the Toll Bridge Seismic Retrofit Account for amenities.