Streets and Highways Code § 192
ARTICLE 5. Funds for Highway and Public Mass Transit Guideway Purposes
In apportioning the State Highway Account money as required by this article, there shall be excluded, from the computations of moneys expended, any sums contributed by any person or governmental unit to pay any portion of the cost of constructing, improving, or maintaining any state highway.
Except as otherwise permitted in this article, any annual or biennial balances remaining unexpended to the credit of any particular county group shall remain credited to such county group.