Literally every study conducted on Mass transit shows the return on investment in heavy rail is JUST NOT COST JUSTIFIED. Atlanta is the least densely populated area with a mass transit system, and its effect on traffic congestion is virtually ZERO.
Folks, it's just not worth paying for another make-work jobs program for MARTA unions to pay for an overpriced service that will NOT HELP TRAFFIC!
Take less than 2% of the cost to build this extension and sync the traffic lights. You'd immediately feel the benefits of that for MUCH MUCH less money.