This was so predictable. There are numerous studies showing that increasing the capacity of roads increases traffic even more. So a short time after the road is "improved" the traffic is worse than before.
--pws
Interactive graphic Commuting times --pws
Big Dig pushes bottlenecks outward
While the Big Dig achieved its goal of freeing up highway traffic downtown, the bottlenecks were only pushed outward, as more drivers jockey for the limited space on the major commuting routes. Many motorists going to and from the suburbs at peak rush hours now spend more time stuck in traffic. (By Sean P. Murphy, Globe Staff)