The two-year study into Hoddle Street traffic was due for completion in the middle of this year.

Money has been re-routed to a $6.5 million study on a Doncaster train line proposal, and as an interim measure the Coalition will consider a bus lane for Hoddle Street.

The bus lane would mean lopping trees and banning car parking on the street.

VicRoads Hoddle Street Study director Agnelo Duarte said the study's "broad solutions" could not proceed to detailed plans without certainty over the train line, which would impact Hoddle Street traffic.

As such, outcomes of the Hoddle Street Study will be postponed for more than two years.

Department of Transport spokeswoman Andrea Duckworth could not say when the Doncaster rail study would be complete.

Yarra mayor Alison Clarke said she supported the Doncaster rail proposal but said there was disappointment at the lack of progress on Hoddle Street. "Community members and council officers have spent more than a year participating in the Hoddle Street study, so it is a pity that at this stage, little appears to have been gained," Cr Clarke said.

While long-term improvements for Hoddle Street are on hold, the Department of Transport is looking at short-term plans for peak-time bus lanes to improve bus travel.

BusVic transport planning manager Chris Loader said Hoddle Street was long overdue for dedicated bus lanes, but said the short-term solution would not negate the need for a large-scale overhaul. "If we want to truly transform Hoddle Street, then even greater separation of public transport from congested traffic is required," he said. "This might involve a special busway – a segregated roadway for buses only – where buses only have to stop for passengers."