Recently, the Georgia Department of Transportation has begun to allow motorists to use the emergency shoulder on segments of GA-400 as traffic lanes during rush hour. GDOT thinks this will reduce traffic congestion on a heavily travelled road. However, the experience so far has been less than encouraging (AJC: Ga. 400 shoulder opens, traffic still a bear). Some would suggest that it is the media frenzy surrounding the opening of new lanes that has caused the lackluster outcomes.
I would suggest another possibility, however. The Fundamental Law of Traffic Congestion, as theorized by Downs in 1962 (and reiterated in 1992), “states that on urban commuter expressways, peak-hour traffic congestion rises to meet maximum capacity.” Recent empirical research by Gilles Duranton and Matthew A. Turner seems to confirm this proposition that adding new traffic lanes to highways does little to reduce traffic congestion. Rather, the provision of new highway capacity is met with a proportional increase in traffic. Therefore, it is unsurprising that the provision of one extra highway lane during peak traffic times fails to reduce traffic congestion.