"The same subway car set was recycled for all the subway scenes in this episode. The crew merely decorated it with different posters to differentiate the scenes that featured the set. To create the illusion of a rocking subway ride, several stagehands stood on either side of the car's outside walls and rocked it back and forth with 2x4s. The set was on loan to NBC from another studio, and on the set's return to its original soundstage, the truck carrying the set accidentally destroyed it while traveling under an overpass that was too low. The set was rebuilt and is still used." [seinfeld.wikia.com]