The commission may, by resolution, provide a plan under which the department may invest presently unneeded money in the State Highway Account in bonds or interest-bearing notes or obligations of the United States for which the faith and credit of the United States are pledged for the payment of principal and interest, in time bank deposits in eligible banks described in Section 16500 of the Government Code, in deposits in eligible savings and loan associations described in Section 16600 of the Government Code, or in any securities of federal agencies described in Section 16430 of the Government Code. The department may, with the approval of the State Treasurer, invest such excess funds in accordance with the resolution. All such bonds, notes, or obligations purchased under the provisions of this section shall be delivered to the State Treasurer, who shall keep them as a portion of the State Highway Account, and all interest thereon when collected shall be paid into and become a part of the State Highway Account.
All investments made under this section shall be liquidated as soon as the funds invested are required for state highway purposes.