A feasibility study completed in 1975 identified the unit costs of guideway options, including the estimation of ‘typical section’ per-linear-foot costs for six guideway types: (1) cut-and-cover subway; (2) tunnel bore; (3) ‘aerial line’; (4) open-cut line with retaining walls; (5) sidehill berm cut line; (6) at-grade line. In addition, the MTDB's enabling legislation explicitly required the guideway system to satisfy the following criteria, consistent with the principles adopted by the Board: priority consideration shall be given to technologies available and in use; guideway system shall be capable of being brought into operation incrementally; transportation rights-of-way of public entities shall be utilized to minimize construction costs. The adoption of the principles effectively required either a ‘light rail vehicle’ capable of street running (to avoid grade separation), or a commuter-rail like design terminating at the Santa Fe Depot.