CHICAGO (WBBM) – The CTA’s newest ‘L’ cars begin tests on another rapid transit line Monday.

LISTEN: Newsradio 780’s Bob Roberts Reports

After stints on the Red, Green and Blue lines, the prototype cars have moved to the Orange Line.

CTA wants to test them in cold weather as well as hot, to make sure they’re reliable. It also wants to make sure the cars are compatible with the Orange Line’s signals.

The cars are totally different under the floor than anything else the CTA operates. They have alternating current motors instead of direct current. As a result, CTA officials said, they cannot run in the same train as older cars.

The cars, being built by the Canadian manufacturer Bombardier, will be tested on all eight of the CTA’s rapid transit lines before production goes forward on the other 396 of the cars in the order.

CTA holds additional options for nearly 300 additional cars, including cars earmarked for a controversial Airport Express service.