The deviation avoided the steep grades with a more winding route featuring sharp curves, deep cuttings, new tunnels and a curved viaduct over Stanwell Creek that required three million bricks in its construction. The old route's ruling grade of 1 in 40 was faced by up (Sydney bound) trains almost all the way between Stanwell Park station and Otford. Although the new route was longer it reduced the ruling grade from 1 in 40 to around 1 in 80. Many stations in this section were closed or rebuilt on the new alignment The Helensburgh Tunnels refer to a series of seven, now abandoned, tunnels between Waterfall and Otford. These tunnels, approximately in total, were built between 1884 and 1886 and were part of the original alignment of the rail line. They were abandoned by 1920 when the new line was built. The main problem was the -long Otford Tunnel, which took the railway through Bald Hill from the coast at to the Hacking River valley. The steep grade and tight clearances meant that soot, smoke and heat could become unbearable, especially when a south-easterly wind blew into the southern portal or when a train stalled in the tunnel. A Mr B. Chamberlain wrote about a stalled passenger train in 1890: Even with the windows closed, the carriages were filled with smoke and steam, women fainted and children screamed until the train backed down to Stanwell Park, and was finally staged up to Otford in two trips. Regarding the crew, Chamberlain wrote: While the passenger with closed windows in an up train had an unpleasant journey... the unfortunate enginemen underwent a shocking ordeal. On tender engines both knelt on the footplate, coats over heads, to breathe the air coming from under the engine, the apron plate being raised for this purpose. Though the air was hot from passing around or through the ash pan, it was nonetheless welcome. Attempts were made to overcome the problem with a ventilation shaft and chimney in the early 1890s and a blower system installed in 1909. List of tunnels The full list of the Helensburgh Tunnels is: The Clifton Tunnel is an eighth tunnel in this section and built around the same time as the Helensburgh Tunnels. Unlike the others it remains in use and is the only single track section between Sydney and . The Metropolitan Tunnel features the first Helensburgh railway station at