Drug taking is so common on Birmingham buses that one route is known as the marijuana express, a city councillor has claimed.
Paul Tilsley said dwindling bus patronage would never be reversed until drug problems were overcome.
He singled out Travel West Midlands' number 50 service, from Birmingham city centre to the Maypole, which had an "appalling" reputation.
Coun Tilsley (Lib Dem Sheldon), the deputy leader of Birmingham City Council, added: "Cannabis is smoked at will. The bus regularly stinks of it. Until we start to deal with these issues the number of people using buses will continue to decline."
West Midlands councils have set a target to increase bus use by ten per cent over the next seven years.
But the region is already losing Government grants because it has not delivered required improvements in the use of public transport.
Coun Tilsley added: "You only have to pick up a local newspaper and look at the letters page to see why bus patronage is reducing."
He urged TWM, the region's largest bus company, to take firmer action against the drug problem.
"This is a company that makes 25 per cent gross profit when the norm is 12 per cent. I am sure they could act very positively to make bus travel a more pleasurable experience," Coun Tilsley added.
Travel West Midlands spokesman Phil Bateman said the bus company was actively tackling crime.
TWM had invested heavily in on-board CCTV systems and was working with the police. More than 800 people had been arrested for a variety of offences, including the use of drugs, since the security clampdown began.
"Complaints about passengers using drugs on board buses in the West Midlands fell during 2005. We do work hard at reducing crime," Mr Bateman added.