California Code, Streets and Highways Code - SHC § 2459

If the actual cost of the project is less than estimated, the allocations made for such project shall be reduced accordingly and the excess shall revert to the fund set aside for the purposes of this chapter.  If the actual and necessary cost of the project exceeds the estimate, the allocations made for such project shall be augmented proportionately by a supplemental allocation.  An allocation, however, need not be made for a supplemental allocation, unless the commission is satisfied that funds would have been allocated for the project had the actual costs been used in determining its ranking on the priority list.