Return on investment

So, we want to move 100,000 people from the East into the city. Every day.

Spend $850M on rail (also taking them off the Eastern Freeway in the process so making it easier for people have have to drive for whatever reason). An extra $300M would link it to the Metro rail tunnel in Parkville.

or

Spend $5B to $9B on an East-West car tunnel, which would bring more cars.

Seems easy doesn't it?  Even if the $850M is concervative, you're still talking about a big difference in money, and in outcomes.

Read here - http://www.theage.com.au/victoria/doncaster-railway-line-could-be-built-for-840m-20120723-22kpg.html