This is one of the more expensive episodes in the series because a replica of parts of the Boston subway had to be built from scratch. Robert Patrick called the set "the biggest damn thing I'd seen in my life."
1013 reference: At the beginning when the officer suspects a fare-jumper, he reports it as a "possible 1013."
In real life, the Boston subway system is called the T, short for the Massachusetts Bay Transportation Authority. In the story, the "T" was changed to an "M" because the LA subway system, which uses the M on its subway cars, was doubling for the Boston subway system.