Va. Code § 15.2-2324
The value of any dedication, contribution or construction from the developer for off-site road or other transportation improvements benefiting the impact fee service area shall be treated as a credit against the impact fees imposed on the developer's project. The locality shall treat as a credit any off-site transportation dedication, contribution, or construction, whether it is a condition of a rezoning or otherwise committed to the locality. The locality may by ordinance provide for credits for approved on-site transportation improvements in excess of those required by the development.
The locality also shall calculate and credit against impact fees the extent to which (i) other developments have already contributed to the cost of existing roads which will benefit the development, (ii) new development will contribute to the cost of existing roads, and (iii) new development will contribute to the cost of road improvements in the future other than through impact fees, including any special taxing districts, special assessments, or community development authorities.
Va. Code § 15.2-2324