I wrote earlier here  about why the removal of the traffic rotary in front of the Sagamore Bridge will not have the intended effect of eliminating traffic on the way from Boston to Cape Cod.
I have a longer piece in today’s Boston Globe  on the same topic. Some people misunderstand my argument. The main point is that eliminating the rotary is likely to have a disappointingly small effect on the time it takes to get from Cape Cod to Boston. It might be so small as to be zero. Most people presume that if there’s a bottleneck (and the rotary is indeed a bottleneck), then if you eliminate the bottleneck, smooth sailing will ensue. My point is that the rotary is the bottleneck today. Eliminate and another bottleneck or series of bottlenecks will occur. Why? When you underprice something, congestion inevitably rations it. Don’t count on smooth sailing.
That doesn’t mean it’s always a mistake to widen roads or get rid of bottlenecks. It does mean that you shouldn’t naively assume that you will "solve" the traffic problem.