Traffic in Melbourne's north could grind to a halt if Opposition Leader Matthew Guy's ambitious proposal to build two massive new toll roads simultaneously gets the green light, the RACV has warned.

The Coalition is investigating the possibility of combining the North East Link road project with a rebooted East West Link if elected at the end of 2018. But Mr Guy emphasised that the controversial $5.8 billion East West Link - which was spiked by the Andrews government at a cost of more than $1 billion - was his party's priority.

An image of the proposed North East Link tunnel, released by the government. Credit:North East Link Authority

Powerful roads group the RACV said the North East Link was needed before the East West Link, and public policy manager Bryce Prosser warned of traffic chaos if roadworks shut down too many existing routes at once.

"There will massive disruption to the residents in the north and the north-east getting to and from the city for a long period," Mr Prosser said.