The Liberals have promised millions for high speed rail studies, and Labor says it will make public transport free for school kids.

Now the NSW Greens have upped the stakes on grand election promises of the transport variety, with a policy to slash Opal fares on metro trains, buses and ferries to $1.

NSW Greens MP Jenny Leong says the policy will "revolutionise" the public transport system. Credit:Dominic Lorrimer

It sounds too good to be true - and the government is emphatic it is - but the NSW Greens are confident their sums add up.

The Greens estimate their "$1 fares for everyone" policy would cost $750 million per year, and say it would be largely offset by increased patronage on the public transport system and by relocating funds from the state's roads budget.