The Main Line is a railway line in South East Queensland, Australia. It was opened in a series of sections between 1865 and 1867. It commences at Roma St Station in Brisbane and extends west 161 km to Toowoomba. It is the first narrow gauge main line constructed in the world. The section of the line from the end of Murphys Creek railway station to the Ruthven Street overbridge, Harlaxton is listed on the Queensland Heritage Register. The Murphys Creek Railway Complex, the Lockyer Creek Railway Bridge (Lockyer), the Lockyer Creek Railway Bridge (Murphys Creek) and Swansons Rail Bridge are also heritage listed.
History
The section from Ipswich (a city about from Brisbane) to Grandchester (originally Bigge's Camp) was the first section of railway line opened in Queensland, on 31 July 1865.
Queensland Railways (QR) was the first operator in the world to adopt narrow gauge (in this case ) for a main line, and this remains the system wide gauge within Queensland today.
The colony of Queensland separated from New South Wales in 1859, and the new government was keen to facilitate development and immigration. Improved transport to the fertile Darling Downs region situated west of Toowoomba was seen as a priority. As adequate river transport was already established between the capital Brisbane and the then separate settlement of Ipswich, the railway commenced from the latter locality and the initial section, built over relatively flat, easy country opened to Bigge's Camp, at the eastern base of the Little Liverpool Range, on 31 July 1865. Called the Main Line, the only significant engineering work was the bridge over the Bremer River to North Ipswich.
Built by the Queensland government to the unusual (for the time) gauge of , the line largely followed the alignment surveyed by a private company, the Moreton Bay Tramway Company, which had proposed to build a horse-drawn tramway but had been unable to raise funds to do so beyond an initial start on earthworks.
The adoption of narrow gauge was controversial at the time, and was largely predicated by the government's desire for the fastest possible construction timeframe at least cost. This resulted in adoption of sharper curves and a lower axle load than was considered possible using standard gauge, and an assessment at the time put the cost of a narrow gauge line from Ipswich to Toowoomba as 25% of the cost of a standard gauge line. In a colony with a population of ~30,000 when the decision was made, it is understandable.
First tunnels
Beyond Grandchester, the line was built with curves of radius and uncompensated grades of 1 in 50 (2%), giving an effective grade of 1 in 41 (~2.5%) on radius curves. Two tunnels were required on the section to Laidley, known as 'Six Chain' (either because it is situated on a radius curve, or because it is to be exact) long, or both) and 'Victoria' after the English Queen of the day. The latter is long, and both remain in service, being the oldest single track railway tunnels still in use in Australia.
From the western portal of the Victoria tunnel the line descends at 1 in 50 to Laidley and then over relatively flat (1 in 100 maximum grades) easy country to Gatton (opened 1 June 1866) and Helidon (opened 30 July 1866). This section was duplicated in 1913–14, with the section from Laidley to Yarongmulu (just west of the Victoria Tunnel) being built to 1 in 60 for Brisbane bound trains.
Surmounting the main range
From Helidon the line climbs in up the Main Range to the summit at Harlaxton [ above sea level (asl)] at an average grade of 1 in 70. However, as the maximum grade is 1 in 50 uncompensated with radius curves, the ruling equivalent grade is 1 in 41, and the maximum speed on the entire section is . This section was opened on 30 April 1867. As built the section contained 157 cuttings (up to long and deep), 128 embankments (up to long and high), 47 bridges (total length , up to long and high), 175 culverts, 9 tunnels (total length ), 49 curves of radius and a further 77 curves between and radius, with a total length of , or 68% of the section.
Comment on the design
A 1995 report commissioned by QR to investigate improving the clearance (loading gauge) through the tunnels so high ISO containers could be accommodated includes a section commenting on the original design. It states that:
It goes on to comment on the Main Range section that:
In 2013 QR called tenders for the lowering of the 11 tunnel floors to enable ISO containers to be carried when the work is completed, expected to be by 2015.