Although it is probably better known as “Coalcliff Tunnel” or “Scarborough Tunnel”, as those are the two nearby Cityrail Stations, the southern portal for the tunnel emerges at Clifton. Clifton station may have closed down in 1915, but the areas influence on the railway line is much more interesting than a closed station.
Clifton, at the south end of the Clifton Tunnel is a small town established by the discovery of coal in the “coal cliffs” of Coalcliff. Coalcliff was a small town established just north of Clifton. Coal mining commenced at the cliffs in 1878. The railway arrived in 1887, from Wollongong (unlike most railway links to towns, the “South Coast Line” went from Kiama to Clifton via Wollongong, while most other railways under construction at the time were branching out from Sydney). Coalcliff station wasn’t opened until 1920, although the railway line had been through in 1888.
Coalcliff has the remains of an extensive yard, which was used up until 2007 by a single train a week, servicing the Coalcliff Cokeworks owned by The Illawarra Coke Company (they also own a cokeworks in Corrimal, next to the station. This cokeworks once had rail access also).
Clifton Tunnel is a single track, kilometer long tunnel between Coalcliff and Clifton. This tunnel remains single track because the land around it is so unstable that drilling a second portal through the hill would be very dangerous. The resulting single track on a double track mainline that sees a frequent Cityrail service, as well as quite a few coal trains (and the occasional Manildra train) often is the cause for headaches.
Often trains will be held on either side of the tunnel, as frequently two trains will be in the area at the same time. Often, if a northbound train is running late out of Scarborough, it will hold up a southbound train from the city, as it was timetabled to clear the tunnel before the southbound train arrived. The southbound train is usually held back before the platform, to prevent passengers thinking it is a scheduled stop and trying to board/disembark (and then complaining about it later).
Due to the large amount of traffic, and the delicate timetable required to cross at the tunnel, often freight trains will be refuged in Thirroul Yard or Coalcliff yard to allow Cityrail trains a priority, especially when close to the peak curfew time in the metropolitan area.
Delays at the tunnel are usually caused by late running trains, as stated above. Last running trains are especially a problem on this line due to the single track section between Unanderra and Nowra. Although there are crossing loops, not all of them can hold a long train, and delays at these crossing loops will have a flow on effect to trains that need to cross at Clifton Tunnel.
However, Clifton Tunnel has been single track for quite some time, and Railcorp and Cityrail have become quite adept at working around it. Unless there are delays somewhere else on the line, often a train that approaches the tunnel will be able to coast straight through it, and if it does encounter a red signal, only for a few minutes.
This post comes again with my thanks to my anonymous friend inside Railcorp, without whom I would know none of these interesting little things we take for granted.