When roads are shut or restricted for construction of major infrastructure projects they should stay that way to take advantage of peoples' revised travel habits, a Monash University engineering and traffic expert says.

A number of major transport projects across the central city have reduced traffic flows, with the most high profile change being February's reduction of St Kilda Road in a key section from three lanes in each direction to one.

St Kilda Road has been cut to just one lane in each direction near the Shrine of Remembrance. Credit:Jason South

That road restriction will last for four years, impacting some 30,000 cars that have until now travelled along St Kilda Road each day between the city and Toorak Road.

Another new road closure is a section of Grattan Street in Parkville, which will be completely shut for five years due to the Metro Tunnel rail project under central Melbourne.