The rolling stock of the Bay Area Rapid Transit (BART) system consists of 782 self-propelled electric multiple units, built from four separate orders, along with a number of automobiles used by BART police and others. To run a typical peak morning commute, BART requires 579 cars. Of those, 535 are scheduled to be in active service; the others are used to build up four spare trains (essential for maintaining on-time service). At any one time, the remaining 90 cars are in for repair, maintenance, or some type of planned modification work. All trains on the separate automated guideway transit line are in regular use without spares. Bombardier Transportation is manufacturing a complete replacement of the mainline fleet, due to be delivered in batches by Fall 2021. The first ten cars of this re