The Victorian Government says it does not know whether its early bird train travel plan in Melbourne is helping to relieve overcrowding.

An extra 2,000 people a day are travelling before the morning peak since the scheme was introduced.

The Public Transport Minister, Lynne Kosky, has told a parliamentary committee it is not clear whether people are changing their travel times or whether drivers are switching to trains.

"We still don't know how many of those are transfers and how many of those are new, new passengers, but that's the equivalent of more than two six-car sets, so it is making a significant difference,"