"How did Transurban get such a good deal at the expense of the taxpayer?"

It was an excellent question, put by Opposition Leader Matthew Guy on Tuesday, about the deal cut between Premier Daniel Andrews and the toll road giant for the West Gate Tunnel.

The contract to build the road through Melbourne's west was signed about 8pm on Monday.

It stands to bring Transurban revenue upwards of $15 billion – perhaps much more. On Tuesday, we discovered Transurban would contribute $4 billion to its construction costs.