That is Walong Siding, and it was used just like any other siding on a single track railroad, to meet two trains.
Walong siding was originally built in 1909 on just the upper portion of the loop. Eventually it was extended to the east portal of Tunnel #9, wrapping completely around the loop itself. This original Walong siding was only 4,800 feet long, which is not long enough for most trains today. An extension connecting Walong with former Marcel siding was completed in 2016, adding another mile of length to the siding.
A section of track for helpers to get out of the way would be a short siding, just a few engine lengths long, maybe even stub-ended, often called a "helper pocket."
