The Napthine government has tied its political fortunes to a multibillion-dollar toll road in a budget that ramps up debt and unleashes $6.1 billion of infrastructure spending ahead of next year's state election.

In a big-spending budget emphasising strong economic management and infrastructure investment, Treasurer Michael O'Brien promised the first stage of the controversial east-west road link – connecting the Eastern Freeway to the Tullamarine Freeway – would begin in late 2014 and be completed in 2019.

The link, which will include tolls, is expected to cost between $6 billion and $8 billion, but it remains unclear how it will be funded, with no business case or submission to Infrastructure Australia released for independent scrutiny.

The government has promised to spend $224 million next financial year and $70 million the following year to complete detailed planning and begin procurement and early works for the road, which will run under Alexandra Parade, the cemetery and Royal Park.