The wooden Leap-the-Dips amusement park ride in Altoona, Pennsylvania, is the oldest roller coaster still running in the United States. Built in 1902, it became a National Historic Landmark in 1996.
It's known as a side-friction roller coaster, a type so outmoded that only a handful of vintage amusement parks worldwide still have one. The key to the ride is a set of wheels that roll and bounce against a vertical plane to keep the cars on their track.
Some roller coaster fans were surprised to see the same set-up used in the futuristic Loop test tunnel unveiled Dec. 18 by Boring Company founder Elon Musk. In the roller coaster world, at least, the tech has been supplemented for nearly a century by up-stop or under-friction wheels, which ride beneath the track parallel to the main wheels as a fail safe.