Sydney's rail fares could double, according to findings of a draft review by the state's independent pricing regulator.

The Independent, Pricing and Regulatory Tribunal this month released a new economic analysis into the benefit the public receives from subsidising public transport fares.

IPART analysis produces a dramatically lower estimate of the public benefit derived each time a passenger catches a train in Sydney. Credit:Daniel Munoz

The analysis produced a dramatically lower estimate of the public benefit derived each time a passenger catches a train in Sydney, which the regulator says it will now adopt.

Regular annual increases to public transport fares will kick in on Sunday, January 4. The new fare settings will increase the gap between the cost of travelling on an Opal card and buying paper tickets.