The Hogwarts Express
The Hogwarts Express is a passenger train which makes a run between King's Cross Station, London, and Hogsmeade Station. It makes this run at least four times a year, and probably more often than that, as needed. It does leave without fail on September 1 at 11 am from Platform Nine and Three Quarters, King's Cross, arriving at Hogsmeade Station in the early evening. Most students take the train back to King's Cross to go home for the Christmas and Easter holidays. The train also makes the run back again to London at the end of term in June.
The train is pulled by a scarlet steam locomotive. There is no dining service, but a witch pushes a tea trolley through the train midway through the trip, selling various types of sweets and iced pumpkin juice. There is a separate car or two at the front of the train for Hogwarts Prefects. There are usually no adults aboard the Hogwarts Express except the witch with the tea trolley and the driver. (PS6, CS5, PA6, GF11, OP11, HBP11).
In the first film, the number on the engine was 5972 (PS/f).
Essays: How Does a Scarlet Stream Train Travel the Length of Britain Without Being Seen? by Steve Vander Ark