Uber is preparing to test a monthly subscription service which will enable passengers to pay a flat fee for each journey.

Under this programme, users can pay a single monthly fee and then a fixed, lower amount for each journey, regardless of the distance or any surge pricing – at least, up to a journey price of $20.

In San Francisco, one of the six US cities where the new system is being trialled, the monthly fee will be $20 (£15) for 20 rides, $30 for 40, and then $2 for each Uber Pool rideshare or $7 for an Uber X taxi. That means, for 20 Uber X journeys made withing a single month, the subscriber would pay a total of $160 – a potential saving of $240.

These prices vary from location to location. As well as San Francisco, trials will launch in Boston, Miami, San Diego, Seattle and Washington DC.

The trial will initially be available on an invite-only basis – in fact, it was one of these invite emails that first tipped off Business Insider to the launch. “Were always thinking about ways to make Uber an affordable, everyday option, and this is a small beta were running as part of that effort,” an Uber spokesperson told the publication.