When MARTA's new rail system opens in December, 1978, commuters will be able to transfer freely between bus and train without paying an extra fare.

"Our goal is a comprehensive, total transportation system with as few barriers as possible," said Alan K. Kiepper, MARTA's general manager.

MARTA train stations will have fare gates that accept either cash or a travel card. If one transfers from the bus and has to go through the gate, the bus driver will issue a card that will open the train gate.

There will be no exit gates from the train stations because MARTA is planing a flat fare system: it will cost the same no matter how far one rides.

(On Washington's Metro, the subway fare is based on distance traveled. The charge cannot be determined until a rider reaches the destination, hence the need for exit gates.)

Half of MARTA's train stations will be patterned after those in Toronto: there will be special bus ramps leading directly to the train platforms. Commuters can just walk across the platform and board the train without stopping for escalators or fare gates.

MARTA's Kiepper concedes a debt to both Washington's Metro and San Franciso's B A R T - the other two new rail systems in the United States - for teaching it some things not to do.

One of the toughest decisions was political as well as technical. MARTA rejected an offer by Rohr Industries to sell it a slightly modified Washington Metro rail car because MARTA engineers did not like many of the features of the Washington car.

The politically tough part of that was that Rohr's factory is only 50 miles away, in Winder, Ga., and the Rohr proposal had the support of several important Northeast Georgia legislators.

MARTA wanted a somewhat taller car (Metro's is lower than most so that money could be saved by digging shallower tunnel), MARTA wanted a different braking system (Metro has had nothing but trouble with its brakes) and MARTA wanted the cars designed with a slight hump in the middle so that the cars would be level with a full load. (METRO's cars sag under a full load, as was designed, but that sagging has sometimes cased doors to stick open.

Although the estimated cost of building MARTA has increased over the years, there have been no cost overruns on the contracts awarded so far. MARTA extracted a no-strike pledge from the construction unions. Strikes have been a key factor in Metro's overruns.