It only took a few painted stencils on the road surface to uncork one of Melbourne's worst tram bottlenecks.

Smith Street, for so long a nightmare crawl for commuters travelling into the city on tram route 86, has begun to flow more freely for tram passengers, though perhaps not motorists.

The new line markings for trams on Smith Street between Alexandra and Queens parades. Credit:Pat Scala

The reason: a series of four bright yellow stamps have appeared on the roadside, directing motorists away from the tram tracks and into the left-hand lane in the morning peak.

VicRoads added the stamps to the northern end of Smith Street, between Queens Parade and Alexandra Parade, in February as a six-month trial.