The Cambridge Subway began service in 1912 with 40 all-steel motor cars built by the Standard Steel Car Company, and 20 cars from the Laconia Car Company.
They had a novel design as a result of studies about Boston's existing lines, with a then-extraordinary length of 69 feet (21 m) over buffers, and a large standee capacity, while weighing only 85,900 pounds (39,000 kg).
They had an all-new door arrangement: three single sliding doors per side evenly distributed along the car's length so that the maximum distance to a door was around 9 feet (2.7 m).
Upon their debut, the new subway cars were the largest in the world; they remained so until the Toronto M1 cars were built in 1962.
A similar configuration was later adopted by the BMT's Standard cars in New York and the Broad Street Subway cars in Philadelphia.

About 20 feet (6.1 m) of the Boston car was separated by a bulkhead for a smoking compartment.
In contrast to the elevated lines, passenger flowthrough was not intended, and every door was used as both entrance and exit.
Thirty-five cars of similar design were added in 1919 from the Pressed Steel Car Company, followed by 60 more in 1928 from the Bradley Car Company for the Dorchester Extension.
The Cambridge Subway began service in 1912 with 40 all-steel motor cars built by the Standard Steel Car Company, and 20 cars from the Laconia Car Company. They had a novel design as a result of studies about Boston's existing lines, with a then-extraordinary length of 69 feet (21 m) over buffers, and a large standee capacity, while weighing only 85,900 pounds (39,000 kg). They had an all-new door arrangement: three single sliding doors per side evenly distributed along the car's length so that the maximum distance to a door was around 9 feet (2.7 m). Upon their debut, the new subway cars were the largest in the world; they remained so until the Toronto M1 cars were built in 1962. A similar configuration was later adopted by the BMT's Standard cars in New York and the Broad Street Subway cars in Philadelphia.
About 20 feet (6.1 m) of the Boston car was separated by a bulkhead for a smoking compartment. In contrast to the elevated lines, passenger flowthrough was not intended, and every door was used as both entrance and exit. Thirty-five cars of similar design were added in 1919 from the Pressed Steel Car Company, followed by 60 more in 1928 from the Bradley Car Company for the Dorchester Extension.
Red Line (MBTA)