AUSTIN — The Austin Transit Partnership board is scheduled to decide Monday whether to abandon a proposed downtown headquarters move and instead expand its existing offices at 203 Colorado St. The revised plan would add the neighboring space at 201 Colorado St. and cost just under $20 million over four years, according to a board memo. That is less than half the approximately $47 million ATP previously considered spending to relocate to another downtown office building. The expansion is expected to take about six months. ATP says the combined space would provide roughly 55,000 square feet for about 280 people working on Austin’s first light-rail system, including staff and representatives from Austin Rail Constructors, Kiewit Austin Partnership, Capital Metro and the city. The proposed headquarters would include 45 offices, 235 assigned workstations, 20 unassigned workstations and 22 conference rooms. The memo also cites parking for some personnel and work vehicles, access to multiple transit modes and proximity to the planned light-rail alignment as reasons to remain downtown. The decision follows criticism of the earlier relocation plan from Austin Mayor Kirk Watson, who serves as ATP’s vice chair. Watson said in April that spending nearly $50 million on new offices was inappropriate while the city faced budget pressures and cuts to essential programs. He urged ATP to explore sharing space with Capital Metro. ATP said it considered that option but was not told until May that the neighboring building would become available. Once the adjacent space opened up, the agency concluded that staying and expanding at its current location was the most cost-effective choice, according to the memo. The board is also scheduled to vote on $122 million for Austin Rail Constructors to continue designing and eventually building the light rail’s tracks, stations and other system components. The board approved an initial $60 million design-build contract with the company earlier this year. Another proposed $44 million would go to Kiewit Austin Partnership for construction of the system’s maintenance facility, where trains will be cleaned, serviced and prepared for daily operations. ATP previously approved $25 million to advance work with Kiewit. The board meeting is set for 9 a.m. Monday at ATP’s headquarters at 203 Colorado St. The votes will shape both the agency’s near-term spending and the operational infrastructure supporting Austin’s long-delayed effort to build its first light-rail line.