Outraged motorists said the Princes Bridge bike lane would add an extra 10 minutes, or even 20 minutes, to their morning commute.

But new data released by the Melbourne City Council on Thursday has revealed the real figure is less than 50 seconds.

The council recorded more than 200 test runs up St Kilda Road before and after the northbound bike lane was introduced.

The council found it took motorists an average of 12.34 minutes to travel from Dorcas Street to Flinders Street after the number of lanes on the bridge was reduced from two to one.

That's 48 seconds longer than before the controversial bike lane opened in late June.