\r\nThe 7000 series cars will be delivered from 2016 and will replace life-expired rolling stock which is nearing or over 30 years-old. If all options are exercised, the fleet could eventually number 846 cars with a total order value of more than $US 2bn.\r\nCTA has already introduced Bombardier 5000 series trains on three lines, and in late 2011 doubled its order to 706 vehicles. Around 190 of these are now in service, with deliveries continuing at a rate of five cars per week. The first 7000 series is expected to arrive in Chicago shortly after the delivery of the final 5000 series cars. \r\nIn addition to the 5000 series, CTA currently operates four fleets of older trains which still make up the bulk of the fleet, totalling more than 1000 vehicles. If the base order and options are exercised, CTA will replace 400 2600 series vehicles built between 1981 and 1987. Additional orders would allow the replacement of the 3200 series cars built in the early 1990s, and the series 7000 fleet could also support ridership growth and the expansion of the network.\r\nCTA says the order marks a major departure from previous stop-start nature of rolling stock procurement by providing a continuous programme of renewal for the ageing fleet.