On the professional side (if not the general public), a lot of the doom-and-gloom congestion predictions probably come from the way the 4-step model works. As trip generation is traditionally based on demographic/economic factors, its not sensitive to anticipated congestion in terms of trip making, and tend to be peak hour only. So if you halved the capacity on every road in the entire region, you’d still have as many trips being made. You see people making shorter trips and more trips by transit, but you’d also see crazy amounts of congestion; far more than you would in real life, because people would make less trips or shift their time of travel.
So, I agree that the congestion probably won’t emerge to the levels feared, although there will probably be some impacts on adjacent corridors (e.g. per Table 1 in Goodwin, although in a few cases the parallel corridors also dropped). However, I’m not sure that’s the end of the story. Given that travel is a derived demand, I don’t think it makes sense conceptually to look at traffic changes in isolation, but rather in conjunction with how they affect the primary demand (i.e. activity participation for work, school, social, or why ever else someone is travelling in the first place). Why are people making these “extra” trips in the first place? Why are they making them at the peak period? The problem with using aggregate statistics is that they lose all sense of “why”. Aggregate travel volumes are simply the sum of millions of individual people making their own choices, so its important to understand why they’re behaving the way they are.
For example, its obviously faster for a car driver to get to work during offpeak than peak. Any yet, many people still want to travel at rush hour, hence why it continues to exist. Clearly, there is some benefit to people from making this trip at this particular time of day that they perceive exceeds the negative impact resulting from the longer travel times they experience. As much as people hate rush hour, they still choose to travel during this time. Why? Well, maybe you need to interact with your coworkers a lot and so you need to all be there at the same time? Maybe you’re a single parent and working during regular hours means you only have to pay for a few hours of after-school day care, and not for a full-time nanny? Is it because “my boss forces me to work these hours, so I have no choice”?. Well, obviously your boss sees some benefit for your company resulting from you being present for you work activity at those times. You in turn can quit and find a job closer to home or with more flexible hours and cut down on travel time, but it probably just pays a lot less. So you’re just accepting the traffic congestion in exchange for the higher salary and the lifestyle it in turn affords.
All that being said, I don’t have any inherent problem with road dieting, lane reduction, tolling etc. in general, and in some cases am pretty keen on it. But I’m a bit hesitant to immediately embrace the “traffic will just sort itself out” attitude unless there’s a carrot being provided that’s at least as large as the stick being used, because I think we sometimes forget about the “why” of travel in the first place, and how it spills over into the rest of our lives. For all the people that we “demand manage” off our roads, we need to understand what their activity-participation behavioral responses will be, and what the impacts of these are. For example, when New York had its transit strike a few years ago, and the traffic chaos didn’t emerge, you inevitably got the “its not that bad, I guess we don’t need transit” type of responses from some corners. Again, same flaw. There are negative impacts, they’re just presenting themselves in not as congestion but instead in terms of lots days at work/economic productivity/wages, scheduling hardships, temporarily deferred activities etc. If transit was useless, why did so many people start using it again once the strike was over? Same thing for the viaducts in the case of the Olympics. In both these cases, people actually had to put up with the change, so they had “perfect information” about the alternatives in that sense, not just what they believed to be the impact of the alternatives. And yet, many switched back to their previous patterns. Why?
In the context of the viaducts, what may happen?
People shift to transit? What service improvements are being implemented in conjunction? There’s not much spare capacity. Are people switching because “wow, I never realized how convenient transit is!” or because “well, I don’t have much of a choice because both transit and driving take so long and its going to cut into the time i spend with my family after work either way”?
Businesses realize they can buy their employees transit passes and save on parking, so people make the switch voluntarily? Great! Whatever traffic impacts are incurred are still acceptable in exchange for the advantages of remaining in their current location.
Businesses get fed up and relocate because employees start looking for jobs elsewhere because they hate the commute? Are they moving closer to where the employees live (good), or simply changing existing transit users to car uses because they’re in an office park (bad). If this causes industries to disperse that benefit a lot from clustering (e.g. there’s no other place in the region where they can all find office space so close together), how does this affect agglomeration economies and labour productivity (and by extension tax revenues)? Bad!
Obviously there’s lots more responses (time of day change, people move closer to work etc.), each with their own pros/cons, but you see what I’m getting at here. So yeah, I just think there’s more consideration needed. And of course, the transportation issues are only one impact (albeit a big one) that need to be considered. I’m not trying to take away from other issues/ideas such as what do we do improve the area if we get rid of the viaduct (or what could we still improve if we keep them)? But that probably warrants a different post.