"There's nothing wrong with you that an expensive operation can't prolong." -- Surgeon (Graham Chapman) to Mr. Notlob in Monty Python sketch.Dare to Share:
Making More Pollution PossibleWhen highway construction is undertaken "to ease congestion" the additional capacity is always absorbed by additional usage. Congestion stays the same, but there are more cars traveling and thus more pollution. (This L.A. Times piece has some good info on this well-known effect.) (For more detailed analysis see "The Fundamental Law of Road Congestion" by Gilles Duranton and Matthew A. Turner here.)
This billion-dollar multi-year construction project will enable more people to commute to jobs far from where they live. This is what causes global warming, among other problems.
A substantial part of such a project's environmental impact comes from the larger and more isolated homes that people commute from when they have more highway capacity. These homes require cars for every errand, have thirsty lawns, and are larger and more energy-intensive than city dwellings. So the carbon impact of such lifestyles goes far beyond the gasoline burned during the commute. (This is why Leafs, Volts and Priuses don't reduce their owners' carbon footprints very much--they still live in the suburbs.)