Construction of the San Diego Trolley proceeded incrementally. The initial construction of new track focused mainly in downtown San Diego. The work on the SD&AE railroad track is best described as ‘rehabilitation’. The MTDB replaced 40% of all ties, cropped and welded the jointed rail, constructed electric catenaries, and installed an absolute block signal system. To control costs, the San Diego Trolley ordered only 14 cars, and did not install ‘mimic’ boards or the on-train location equipment until after the East Line was completed in 1989. No new sidings were initially installed on the SD&AE segment, which had three passing sidings between San Diego and San Ysidro. Service started at 15-minute headways using the rehabilitated single-track line.