Ablarc,
Thanx for the link. In reading through it, most of it seemed reasonable, at least in a theoretical sense.
In the actual case of 128 being widened, I do not think there is much fear of it encouraging additional development (as most of the area is fairly well built out already) and therefore would not suffer substantial traffic increases from this potential source. The window to 'zone out' development has long closed in/around 128.
I do think that, over time, the demand would increase to eventually 'use up' the added capacity, but that it will take a long time to do so. I do not necessarily think this is cause to not move forward with the project. Especially given the population density of the area, the amount of commercial activity that relies on the road (for better or worse) and the unlikelihood of any viable public transit option that mimics the route--I wish there was a better chance of this happening and I am very much for expanding all things public transit related, but the reality I think points otherwise.
Perhaps adding in tolls or increased fees (as mentioned in the article) would have the effect of reducing usage . . . the toll issue is a current and separate one though and I'll treat it as such.
In my mind, the scenario that hatched the big dig is not a bad analogy (cost overruns, union incompetence, and moronic corrupt contractors and politics aside). Clearly the Interstate roadways that went through downtown had been maxed out for quite some time and the long periods of bumper to bumper traffic was not good for anyone. Mind you, a decent public transit system was and is in place for commuters coming from a majority of Boston's suburbs. And as alluded to earlier, pretty much all of the land within 128 and a good portion of the land within 495 was and is fairly well developed (yes there is always development going on, but it is not as though greater Boston just sprung up 30 years ago). The argument could be made that many of the closer communites were and are also served reasonably well by the subway and bus lines (and ferries?). So even with viable options for many commuters, there was still traffic (people passing through, commercial traffic, those not served well by public transit, and those that just do not use it). The decision was made to 'do something'.
The finished product of the big dig, now substantially complete for a couple of years with other portions having been done for over a decade (Williams tunnel, for example), has clearly improved the congestion through the city and to the airport. Are there times that it is still bumper to bumper, even without bad weather and/or accidents? Sure, but not nearly as much (my apologies for not being able to provide any emperical data).
Was it 'worth' the cost of the project? Well, that is a subjective question and depends on many factors, notably how you define 'worth'. I would say yes. The cost of having done nothing would probably have already amounted to 15 billion in lost time and fuel (and, resultiningly, business and profits) over the last 20 years.
Again, no hard data but if you multiplied the difference in the number of hours of congestion times the number of people 'caught' in it times some reasonble approximation of an hourly rate and added to that a summation of a likewise reasonable approximation of the extra fuel that would have been used to sit in the traffic over the same period of time I am sure it would be one hell of a big number.
In summary, like the big dig, I think widening 128 will have more of a positive effect than a negative one on congestion. And I think this effect will persist for a fairly long time--we are talking about a 33% increase in roadway capacity . . . I just do not see a commensurate increase in usage anytime soon, especially if gas prices stay above 2.00 per gallon. That said, I do not think it is the perfect or ideal or even a stand alone solution, but I do think it will help.