The Toronto subway cars used for filming cannot operate singly, so a two-car set was used. A phony cab was built on the other end of H-1 car 5482 to simulate single car operation.
The single car supposedly detached from the front of the train can be seen on several occasions to be part of a train of at least two cars. The most obvious cases are when rounding curves: once when first moving forward after being detached, and later when Anthony has just figured out the hijackers' plan.