Interesting. Brunel built an atmospheric railway in Devon as part of the Great Western Line between Exeter and Plymouth. It was a different technology (i.e. no tunnel) but a similar idea. Sadly, it was extremely maintenance heavy and didn’t last long but it did run in live service for a while. I didn’t know any other similar schemes existed before seeing this video. There is a good description of the Brunel Atmospheric Railway on Video 125’s HST West DVD/Video along with the museum at the Starcross Pumping Station (sadly no longer open although the building is still there). Also, for anyone interested in signalling, it was filmed in 1986 and semaphore signalling was still being used.