The 6000 series was a series of Chicago "L" car built between 1950 and 1959 by the St. Louis Car Company. 720 cars were built. The last of 6000-series cars were retired on December 4, 1992. These cars were in service for 42 years.
In 1947-1948 the CTA received four three car articulated trainsets, 5001-5004, to test PCC technology in rapid transit use. Two sets of cars were built by Pullman, two by St. Louis Car, with equipment supplied by competing suppliers, in order to test them directly against each other. The 6000 series was designed with knowledge from the 5000 series.
5000 series bodies had a curved profile previously used by North Shore Line and then Chicago, Aurora & Elgin cars which operated on the L. The floor width was the 8 ft 8 in (2.64 m) needed for platform clearance, then above the sides curved outward, so the car was wider at seat level. This profile was used, 6000 series cars were 8 in (20 cm) wider at the seats than the floor. Blinker doors which fold and open inward were also successful and were used in the 6000 series.
Articulation was not repeated, the 6000s were individual cars semi-permanently attached in pairs. The outside end of both cars had a cab, making a two car double ended arrangement. This has become the CTA standard.
St Louis built all 6000 series cars, as well as the 1-50 series, many with components salvaged from Pullman streetcars.
The 5000s had modified Clark and St Louis trucks with 28 in (711 mm) wheels for speeds of x. The 6000s had more standard streetcar trucks, with 26 in (660 mm) wheels. These had a top speed of 50, which was adequate for CTA needs until the high speed Skokie Swift shuttle started in 1964.
The first 200 cars were built with new components, including Clark B-2 trucks, the next 310 cars had Clark B-2s salvaged from Pullman streetcars, and the final 210, plus most of the similar 1-50 class, had St Louis B-3s salvaged from St Louis streetcars.
All cars had Westinghouse XDA1 controls. 6001-6488 had Westinghouse 1432 motors, all following cars had General Electric 1220 motors. Both type motors delivered 220 hp (160 kW). The exceptions are test cars 6127-6130, which had non-standard equipment and higher performance.
The 6000 series became the standard of the system, and were used almost everywhere. In 1975 there were still over 700 6000s in service.
Initially, all of the first 130 6000s were assigned to the Logan Square line. The North-South and Ravenswood lines had 6000s in service in 1952 (with the 4000-series cars taking the 6000s' place on the Logan Square line); other lines (except the Lake Street line, presumably due to width clearance issues on the at-grade section of the line west of Laramie Avenue, which was also powered by overhead wire) received cars when they became available.
Because of overhead wire, no 6000s were used on the Skokie or Evanston lines, except 6127-6130, which received trolley poles for express service on the Evanston line. (The western section of the Lake line was elevated in 1962; however, it remained equipped entirely with 4000s until the arrival of the 2000-series cars from Pullman-Standard in 1964.) Two of the routes that the 6000s were not used on were served by their single car variants, the 1-50 series. The Evanston line began to receive additional 6000s after it converted entirely from overhead wire to third rail in 1973.
When the Dan Ryan line was opened in 1969 newer cars were assigned there, but 6000s were sometimes used for special movements.
CTA sold some of the cars to SEPTA for use on the Norristown High-Speed Line during the delay of the N-5 car delivery.