Rail trails are based on disused railway lines being ripped up and their relatively level trackways being converted to recreational applications like walking or cycling. The idea really started to gather steam in the mid-eighties in the US, where these days the Rail Trail Conservancy supports about 13,600 miles (~21,900 km) of rail-trails. The concept of railway reuse has spread around world. In Western Australia, for example, old logging lines were converted to make sections of the almost 1,000 km (620 mile) Bibbulmun bushwalking track, which in turn inspired the Mudda Biddi bike trail. On the Australian east coast there is the Murray to Mountains Rail Trail, of which a recent study found that cyclists had brought $2.3 million AUD in eco-tourism to local economies, over a single holiday weekend. As the head of the bicycle advocacy group put it, "It probably cost $4 million to build the Murray to Mountains Rail Trail so they can say they've got half their money back in one weekend." The 94 km (58 mile) trail is a bitumen sealed track utilising the gentle gradients of unused rural railways to bring tourists to a country area, the financial impact of which was described as the same as introducing another crop to the region. ::Murray to Mountains Rail Trail, via the Border Mail.