sentences:  The need for the project arose from the rapid and sustained growth of the northern suburbs of Perth during the 1970s and 1980s, which had placed a considerable strain on infrastructure, including the bus system and the Mitchell Freeway.However, prior to the opening of the railway, the proposal was controversial as many in the community believed that upgrading the Mitchell Freeway or providing a guided busway would be better solutions.The Northern Suburbs Transit System name has been used subsequently for additions to the original line, including the Currambine to Butler extension which was built as far as Clarkson in 2004, and extended to Butler in 2014.