California Code, Streets and Highways Code - SHC § 2209

If the annual apportionment to a county pursuant to Section 2208 is less than 1 percent of the total of such allocations to all counties, the county may exchange its apportionment for an equal amount of nonfederal funds in the State Highway Account in the State Transportation Fund. If the apportionment to a county is more than 3 1/2 percent of the total of such allocations to all counties, the county may exchange that portion of its apportionment in excess of the 3 1/2 percent for an equal amount of nonfederal funds in the State Highway Account. Exchange funds received by a county pursuant to this section may be used for any highway construction purpose.