There will be more riders testing Metro’s new way for uploading money to SmarTrip electronic fare cards.

The transit agency launched a pilot program in July for riders to test the system to add money using credit and debt cards online. Metro is extending the pilot so that more riders can experience the program and so that the agency can gradually ramp up the system before it launches later this month, chief spokesman Dan Stessel said.

The test program has gone from having 250 participants in June to a total of 150,000 this week, Metro said.

The new system is meant to make it “more convenient” for riders to manage the balances on their cards and avoid lines at fare gates and machines, according to a promotion of Metro’s pilot program.

The transit agency is running a competition to hire a vendor to develop a new electronic payment system.

Metro has put out a request for proposals for a vendor to build a program that would use an “open payment system” so that riders could use credit or bank cards directly at fare gates. The technical proposals are due at the end of the month.

Several vendors responded to the request for proposals including, ACS, Accenture, CSC, Cubic, FIS, IBM and Revere Group, according to Metro. The transit authority plans to award the contract in the first quarter of 2012 and phase in the new program from 2014 to 2017.

Officials hope the new system would work with other open payment methods used in surrounding jurisdictions, including Virginia Rail Express (VRE), City of Alexandria’s DASH bus service, Arlington County Transit (ART), TheBus in Prince George’s County and Ride On buses in Montgomery County.

The SmarTrip electronic fare payment cards have been plagued with troubles, with some riders complaining that they stop working or don’t work well in adding passes for bus trips.

“SmarTrip is 12 years old,” Stessel said. “It was state of the art when it was introduced. It is still better than many transit systems, but many transit agencies are moving to open payment because it is more convenient for customers.”

Follow me on Twitter @postmetrogirl.