- "Watch out for the viaduct, it's dangerous!"
- ―Mr. Conductor, Thomas and the Magic Railroad
The Big Dipper is a large two-track viaduct made of stone. When Mr. Conductor was captured by Diesel 10, he discovered that the bridge had begun to collapse as a result of the world losing its energy, caused by his gold dust crisis. It is located north-east of Kirk Ronan, near the Cement Works. The Hawin Croka river runs underneath the viaduct.
The Big Dipper was only seen in the 2000 film, Thomas and the Magic Railroad, however, parts of the viaduct was seen in the Jack and the Sodor Construction Company episodes, Jack Owns Up and Percy Helps Out. David Axford stated on SiF that it may have been the same viaduct.
- The viaduct was only called "The Big Dipper" in the original Thomas and the Magic Railroad script.