All projects reasonably estimated to cost $300,000 or more that the Board or the Commissioner of Highways may undertake for construction shall be let in accordance with the Virginia Public Procurement Act (§ 2.2-4300 et seq.). When such projects are reasonably estimated to cost below $300,000, the Commissioner of Highways may let them to contract, and if such projects are let to contract, they shall be let only in accordance with the Virginia Public Procurement Act. As used in this section, “project” means construction and does not include routine maintenance work or the installation of traffic control devices, unless such work is to be performed under contract.