Both routes provide service between New Carrollton and Greenbelt connecting travelers to both communities without having to enter Washington, D.C. by train.

Route G14 trips skip the Beltway Plaza Mall loop on weekdays only before 7:45 am.

The route then turns and loops into Beltway Plaza before resuming along Greenbelt Road.

The route then turns along Gardenway and Crescent Road serving Roosevelt Center/Old Greenbelt meeting up with the G12.

The G14 remains along Southway before turning on Greenbelt Road serving Greenway Shopping Center which meets the G12 again.

The G14 then remains along Greenbelt Road until turning along Mission Drive, serving Goddard Corporate Park.

[2] Early morning Saturday service was discontinued on September 26, 1977 being replaced with the Orange and Blue Lines with peak hour trips not being affected.

Both routes would primarily run along Greenbelt Road, Cherrywood Lane, Kenilworth Avenue, the Capital Beltway, and John Hanson Highway.

[5][9] On June 30, 2002, routes T15, T16, and T17 routing were changed where buses will operate via Soil Conservation Road to the NASA visitors center outside the security fence at Goddard Space Flight Center with customers can get off the bus at new bus stops along Greenbelt Road near the main gate.

The Metro Board then took all service cuts off the table before approving the budget for that fiscal year.

WMATA staff wanted to reconstructive the routes because they felt that resources could be used more efficiently.

WMATA estimates that proposed changes will save about $563,000 per year in operating costs.

It was set as the following:[20] In September 2010, WMATA released the final proposal for future Greenbelt service along with Prince Georges County TheBus in October 2010.

Route G12 would run between Monday and Saturday (the same as the T16), the G13 was a morning rush-hour service only that doesn't serve Beltway Plaza Mall and has the same routing as the G14, the G14 only ran Monday and Friday from 8:00 AM to 6:00 PM running via Goddard Corporate Park, and the G16 ran Weekday late nights after 6:00 PM and Saturday service only skipping Goddard Corporate Park.

Similarly, someone at Beltway Plaza (G13/G14/16) can reach Roosevelt High or Doctors Community Hospital (G12) the same way.

[29][30] On June 26, 2011, routes G13 and G14 were rerouted in Goddard Corporate Park to operates along Forbes Boulevard and Aerospace Road then return to Greenbelt Road due to provide service closer to an office building at 7700 Hubble Drive housing for NASA and NOAA employees.

Service along Aerospace Road and Forbes Boulevard would be discontinued due to low ridership for route G14.

The reasons for the proposed changes was simplify the Greenbelt–New Carrollton Line, very few people use stops on Aerospace Road, extending all G16 trips to Goddard Corporate Park will provide better service to the apartments on the south side of Greenbelt Road (east of Good Luck Road) and to Eastgate Shopping Center and the route has many riders during the week and Saturday which should have Sunday service under WMATA standards.

[32] On March 27, 2016, routes G13 and G16 were discontinued by WMATA and replaced by the G14 which added weekend service.

The G14 would absorb the G13's Beltway Plaza Mall skip in the morning before 7:30 AM and serve Goddard Corporate Park at all times.

Route G14 would also discontinue service along Forbes Boulevard and Aerospace Road due to low ridership.

In 2017, WMATA proposed to revise the G12 and G14 schedule which would eliminate the Time Transfer at Roosevelt Center.

The G12 and G14 are scheduled to depart from both Greenbelt and New Carrollton within a few minutes of each other and are timed to meet at Roosevelt Center.

WMATA proposed to stagger the departure times because staggering departures at the stations could provide more departure options to customers travelling to and from stops served by both routes, including at Roosevelt Center in Greenbelt, improving the combined frequency of service from approximately every 30 and 60 minutes to every 15 and 30 minutes at stops served by both routes G12 and G14 and would improve service operations and reduce bus congestion at the New Carrollton, where routes G12 and G14 share a bus bay according to WMATA.

An example of the proposed scenario goes as follows:[35] Performance measures according to WMATA go as the following as of the FY2016 budget:[35] On June 24, 2018, the "Timed Transfer" at Greenbelt Center was discontinued by WMATA in order to improve the combined service frequency for customers on both routes.

[42] In August 2022, G12 service temporarily bypasses Doctors Community Hospital due to a safety concern.