NSW Treasury requires a final business case for all projects costing over $5 million. Late last year, the government released an Updated Strategic Business Case which meets some requirements, but not all. Shockingly, despite failing to meet its own processes, the government has already awarded contracts and started construction. The City of Sydney asked SGS Economics and Planning (a company that prepares business cases for tolling companies) to review the updated business case and its response was damning. The company called it "a confused document filled with contradictions." It doesn't properly analyse potentially cheaper alternatives such as public transport and demand management, it selectively over-estimates benefits and under-estimates costs and it ignores the fact that the second airport will change freight and commuter traffic patterns. In comparison, the East West Link Needs Assessment undertaken for the Victorian government carefully examined four options which combined a range of road and public transport options to reduce congestion in Melbourne.

The NSW government has never provided a similar analysis of alternatives to WestConnex. SGS report that any benefit of WestConnex "is likely to be marginal at best and it is quite possible that the actual BCR (Benefit-Cost Ratio) is less than one" – meaning the costs will exceed any potential benefits. Incredibly for such an important project, the updated business case also contains basic mathematical errors and contradictions. Dividing the present value of benefits by the present value of costs brings up a phenomenal half a billion dollar hole. Even using the government's own figures, the estimates show that most drivers will save less than five minutes, and the road network around the toll road and some sections of the tunnel will reach capacity as soon as 2031, only eight years after completion – an appalling return for a $30 billion project. Their figures also show that on key corridors public transport is quicker than driving and will be in the future, too, so it's a fantasy to think that saving less than five minutes will encourage more people to drive, paying hundreds of dollars on road tolls for the privilege.

It's why the Lane Cove Tunnel and Cross City Tunnel projects both failed. Unlike those projects, however, which were owned by the private sector, this time the government will wear the financial risk of WestConnex. And the costs will be measured in hospitals and schools not built, land no longer available for homes and public transport not delivered. WestConnex is diverting funding from public transport which is desperately needed across so much of our city especially in western Sydney, and it actively works against the government's own Metropolitan Strategy, which calls for a number of economic centres in Sydney's west so people can work closer to where they live. It will bring tens of thousands of cars into already congested areas in the inner city and it will put thousands of young children and the elderly at risk by exceeding allowable air pollution levels around the St Peters interchange, right next to one of Sydney's most loved regional parks where they are planning to chop hundreds of trees for the new road. Despite what the NSW Roads Minister says, it is not too late to stop this. WestConnex is a 1950s solution – no other comparable city in the world is currently tackling congestion by building motorways – but this is not just a question about the right way to move people around our city.

This is about the way a government should make decisions about how to spend billions of dollars of taxpayer's money. The government has a moral responsibility to follow proper processes when funding multi-billion dollar projects. They must be able to prove that WestConnex provides better returns for NSW taxpayers than other options such as public transport or demand management. It's time for all work on this project to be suspended until they can do that. Clover Moore is the lord mayor of Sydney.