Starting this Sunday, commuters will no longer have to pay double fare for a journey that involves both the TTC and GO Transit or the UP Express.

Someone who arrives downtown by GO train, for example, will be charged just $1.50 to continue their trip using a TTC subway, bus or streetcar.

That's literally half price for PRESTO card users (who, it should be noted, are the only riders eligible for the program).

"This discount is available exclusively for PRESTO users who pay as they go with their card balance," reads a website explaining how it works. "It is not available if you use a PRESTO monthly pass, cash, paper tickets, tokens or a Metropass on your PRESTO card."

Save even more with PRESTO! Starting January 7 you can save up to $1.50 when you use your PRESTO card and transfer between @TTCnotices and @GOtransit or @UPexpress. Lean more at: https://t.co/6UnlUfzsxJ pic.twitter.com/M0sI0Dqdva

— PRESTO card (@PRESTOcard) December 18, 2017

Card holders don't have to do anything to get a lower fare. Discounts will be applied automatically, in both directions, for all adult, senior and student card holders. 

For adults transferring from the TTC to GO or UP Express vehicles, $1.50 will be shaved off the cost of secondary fares, which range in price based on distance travelled.

Students and seniors will save $0.55 when moving between transit services in both directions.

Metrolinx recommends using its Triplinx route planner starting on Jan. 7 to find out how much your particular journey will cost from start to finish.