[/quote]The killer for rail at the moment is the TAL. 15.something. Madness. Even an increase to only 19TAL would make a difference (lets hope they go for 21TAL though.[/quote]
The problem is, the axle load issue can almost be directly related to the Inland Rail Project - the whole QR network west of Brisbane has been largely in an infrastructure paralysis for the last twenty years as the dream of a new national rail link to replace most of the existing infrastructure has sat on the table. It would be a reasonable assumption that if the Inland Rail concept had never existed, axle load and capacity upgrades would have eventually occurred on the West Moreton, Western and South West systems as had happened on the rest of the Queensland mainline network during the 1990s.
As it stands, the West Moreton system between Brisbane and Toowoomba, with 50kg and 60kg rail on concrete and steel sleepers has sufficient rail and sleeper structure in place to support axle loads up to 26.5-tonnes. The South Western system south of Toowoomba to Thallon has 41kg and 47kg rail on mixtures of all steel, one in two steel and one in four steel, a structure that in North Queensland has been used for 20-tonne axle loads with track speeds of 80km/h. So the track isn't the problem with higher axle loads.
Bridges are no doubt a substantial issue, the South Western system (444km Toowoomba to Thallon) has 119 timber trestles (4053m), 14 steel bridges (573m) and two short concrete bridges (45m). Compare that to the 340km Townsville-Cairns section of the North Coast Line, which has had a 20-tonne axle load since 1996, and you'll find 70 timber trestles (2344m), ten steel (961m) and 94 concrete (4650m). The large number of concrete bridges to Cairns bely the $300-million spent on the section between 1993 and 1996 as part of the Main Line Upgrade Project - a large scale project that has never been replicated west of Brisbane despite three times the tonnage moving over the Toowoomba Range compared to the Cairns section of the NCL. That being said, the large number of trestles still in place between Townsville and Cairns more than prove that the identical bridges south of Toowoomba should be able to sustain a higher axle load than the current 15.75-tonnes.
There may also be a more insidious reason for the lower axle loads - pricing. The Maryborough Branch remains a 15.75-tonne axle load line, but has been carrying 20-tonne axle load locomotives without incident since 1999. How is this possible? Apparently much higher "special access" fees are charged for these overweight movements - so this is one line in the QR Network, built to the same standards as the South Western System, that is "safe" to carry higher axle loads if the price is right rather than being physically constrained to lower axle loads.
I would not be surprised to learn that some lines in the QR Network retain a 15.75-tonne axle load due to bureaucratic intransigence rather than any other better engineering reason.