In the book, they describe the car crossing the George Washington Bridge, which connects northern Manhattan to New Jersey. Just before they get to the Jersey side, the car jumps the divider and heads back to Manhattan and eventually the Bronx. The film holds very close to book. Today you would never jump the divider in a car. The bridge that was used in the film was the Queensborough Bridge - aka the 59th St Bridge, from the same title as the Paul Simon song (Feelin' Groovy). The film crew did not have permission or permits to film on the bridge (budgetary constraints). They devised a plan to block both sides, they drove the vintage cars on to the bridge, quick set up, shot the scene and left traffic jams on Third Ave in Manhattan. Those of us who have driven the GW Bridge know that wasn't the bridge, but it is the only bridge that connects Manhattan with New Jersey. Such is artistic license. There also wouldn't be a sign on the 59th St Bridge "To New Jersey" especially since they would have been heading in the opposite direction.