Hoddle Street will remain a traffic nightmare even after the Napthine government's east-west toll road is completed, according to the Department of Transport.

A department briefing prepared for Roads Minister Terry Mulder says only a small proportion of the cars, trucks and buses clogging Hoddle Street are likely to use the tunnel as an alternative if there are no off-ramps to the city.

Going nowhere: A very congested Hoddle street at peak hour. Credit:Angela Wylie

The finding was mirrored in a November 2011 ''Hoddle Street Study'', released under freedom of information laws. It reveals the department's own traffic modelling found ''no expected change to the traffic operation of Hoddle Street as a result of the new link''.

Rather, it suggested the situation on Hoddle Street, already one of Melbourne's most congested roads, would worsen. With the road already carrying more than 90,000 vehicles a day, it warned worsening congestion triggered by population growth would increasingly force vehicles onto surrounding roads as motorists searched for alternative routes, further clogging the inner north.