Due to the absurdly parochial and arcane manner in which transportation issues are addressed and discussed in Georgia, I have stopped paying attention to the regional T-SPLOST voters in the state will decide in June. Until the final project list comes out in a few weeks, I remain solidly on the fence when it comes to my position of support, for or against.
That said, if I had the undivided attention of every voter in the state, this is the message I would deliver. Adding capacity in the form of new roads or expansions does nothing to ease traffic congestion in the mid-to-long term.
From "The Economics of Traffic Congestion," by Richard Arnott and Kenneth Small as published in American Scientist, Vol. 82, "Any reduction in congestion resulting from capacity expansion encourages others to drive during hours on routes they ordinarily would not use. So measures to relieve congestion are at least partially undone by latent demand.
"The other reason capacity expansion alone does not work is that congestion is mispriced. Because drivers do not pay for the time loss they impose on others, they make socially-inefficient choices concerning how much to travel, when to travel, where to travel and what route to take... The combination of latent demand and mispriced congestion may be so perverse that an expansion of capacity brings about no change in congestion, or even makes it worse."
If you're a real transportation wonk, here's the link to the rather complex article. http://www.econ.ucsb.edu/~tedb/Courses/Ec1F07/traffic.pdf
There's also this little gem about "induced congestion" from researchers at UC Berkeley who found considerable empirical evidence that showed every 1% increase in new lane-miles generated a 0.9% increase in traffic in less than five years (emphasis added).
So dear reader, whenever our transportation "leaders" roll out the project list for which they will ask us to decide whether or not we want to foot the bill, please, please, please remember that ultimately building new roads or adding to existing ones doesn't do a damn thing to relieve congestion.