Starman

Launched in 1977, the Voyager 2 space probe carried a gold phonographic disk with a message of peace, inviting alien civilizations to visit Earth. The probe is intercepted by an alien ship which then sends a small scout vessel to establish first contact with Earth. However, instead of greeting the alien craft, the US government shoots it down. Crashing in Chequamegon Bay, Wisconsin, the lone alien occupant, looking like a floating ball of glowing energy, finds the home of recently widowed Jenny Hayden (Karen Allen). While there, the alien uses a lock of hair from her deceased husband, Scott, to clone a new body for himself as a terrified Jenny watches. The alien "Starman" (Jeff Bridges) has seven small silver spheres with him which provide energy to perform miraculous feats. He uses the first to send a message to his people stating that Earth is hostile and his spacecraft has been destroyed. He arranges to rendezvous with them in three days' time. He then uses the second sphere to create a holographic map of the United States, coercing Jenny into taking him to the rendezvous point in Arizona.
Jenny is initially both hostile and frightened of him and attempts to escape. Having a rough understanding of English language from the Voyager 2 disk, the Starman learns to communicate with Jenny and assures her that he means no harm. He explains that if he does not reach the rendezvous point, Arizona's Barringer Crater, in three days, he will die. Sympathetic but still wary, Jenny teaches him how to drive a car and use credit cards so he can continue the journey alone, but when she witnesses him miraculously resurrect a dead deer, she is deeply moved and decides to stay with him. However, they are pursued across the country by the authorities and, after nearly being caught, Jenny is shot and critically wounded by a police officer. In order to escape, the Starman crashes their car into a gas tanker and uses another sphere to protect the two of them from the explosion. They take refuge in a mobile home that is being towed. He uses another silver sphere to heal Jenny. After being assured that Jenny will recover, the Starman proceeds to hitchhike towards Arizona without her, but Jenny manages to catch up to him while he and his driver are stopped at a roadblock. Reunited, the two of them hitchhike together, resuming their journey towards the crater.
Later, while stowing away on a boxcar train, the couple makes love. The Starman tells Jenny "I gave you a baby tonight." Jenny explains that she is infertile and cannot have children, but he assures her she is now pregnant. He explains that the baby will be the son of her dead husband, because he (Starman) is a clone of Scott, but as a child of Starman as well, their son will possess all of the Starman's knowledge and will grow up to be a teacher. Starman offers to stop the pregnancy if she wishes, but the joyful Jenny embraces him, accepting the gift.
The couple mistakenly travel too far on the train and arrive in Las Vegas. Jenny realizes she has lost her wallet. The Starman uses one of their last quarters in a slot machine, which he manipulates in order to win the $500,000 jackpot. They then buy a new car to complete their journey to Arizona.
Meanwhile, National Security Agency director George Fox learns that the Starman's flight trajectory, prior to being shot down, was to the Barringer Crater. Fox arranges to have the Starman captured by the Army, dead or alive. SETI scientist Mark Shermin, another government official involved in the case, criticizes Fox's heavy-handed approach and reminds him that the Starman was invited to Earth. Appalled to learn that Fox is planning to vivisect the alien, Shermin then resolves to help the Starman escape rather than allow Fox to capture him.
Jenny and the now dying Starman reach the crater as Army helicopters pursue them. Just as they are surrounded, a large, spherical spaceship appears and descends into the crater. Light surrounds the couple, and the Starman is instantly restored to health. As he prepares to leave, he tells Jenny he will never see her again. Jenny begs him to take her with him, but he says she would die on his world. He then gives her his last silver sphere, telling her that their son will know what to do with it. Jenny watches as the ship departs.

Question: Where did the couple stow away on?
Answer: a boxcar train