It's the World's Steepest Vehicular Inclined Plane. One of the few "touristy" things Johnstown has to offer. It is rather neat, though. You can ride up it and it can also transport your car up the steep mountain. Came in handy during two of the many Johnstown Floods.
Here's some more information about it.
And the wikipedia page, since Johnstown isn't very technologically proficient and their webpage is a little lame.