GRTA was established in an attempt to tackle worsening air pollution in the Atlanta metro area under Governor Roy Barnes. The agency was given broad control over the 13-county metro area, with the intention that the agency would tackle regional transit and road planning alike. GRTA was to be able to plan, fund, and build many transit lines and roadways as it saw fit, with the ability to influence other agencies and governmental groups operating in the metro area.
Despite this power, the agency has not grown much beyond a relatively small system of express and commuter bus routes, primarily aimed at the core of Atlanta. As a state agency, GRTA, like GDOT, is at the whim of the legislature's priorities, and has not been well funded to perform its intended, wide-reaching role.
Though the original plan was never fully realized, GRTA currently operates 26 commuter bus routes, and partners with both Cobb Linc and Gwinnett County Transit to operate additional routes. There are no current plans for the agency to operate anything other than express routes, though they have been steadily expanding their eXpress bus services.
Should GRTA ever expand into a larger, regional transit agency as initially intended, it will likely follow its current role as a commuter-based system, moving people from park-n-rides to nodes of employment. It will also likely continue to make use of MARTA's infrastructure as it comes in from beyond the core counties. Commuter rail lines, train stations, regional bus stations, and bus lanes all implemented under MARTA's control would only help support further-reaching services, while saving the agency money. As such, expanding MARTA may very well help GRTA grow in the long run, offering more opportunities to reach out into the further-off metro area.