Tuesday, August 31, 2010

My Letter to VDOT concerning the widening of I-66

To Whom It May Concern:

Let me begin by writing that I truly sympathize with commuters and travelers that need to drive through Arlington. Congestion can be awful on I-66 and it is the case that people often have poor alternatives to driving. Regardless, when I look at the present details of projects #1 and #3, I am pretty skeptical that any improvements are being made with respect to travel time. Given the general local opposition to the project -- I think that there are some valid points among the vitriol ... there are points that I see as more of a rant -- it appears to me that some more thought is needed to address the transportation issue. Consequently, I am opposed to the present plan.

My understanding of queuing theory is that people switching lanes creates more chaotic motion which increases travel times. I think that given the congestion on I-66 that aggressive drivers will use the long auxiliary lane to leave the regular travel lane, advance in the queue, and re-enter the travel lane at some point creating an effect that will -- on the margin -- increase travel times. Now from a conversation with the traffic management person at the 10/27 meeting, the creation of an auxiliary lane gives drivers that enter/exit the highway more space to negotiate their entrance/exit which would decrease travel times. His simulations suggested that the net effect is to decrease travel times.

One problem with the conclusion is that it appears to lack measures of robustness. For instance, if I ask what is the confidence interval of the average difference in travel times, the simulations do not support such analysis. The issue here is that there are competing effects and everyone agrees that the simulations contain considerable uncertainty, but we have zero measures of that uncertainty. Given the aforementioned competing effects, it would not be surprising if a confidence interval existed, it would include zero, as well as, a range of positive values. From the perspective of science, the conclusion that projects #1 and #3 represent an improvement is pretty weak.

A second problem with the conclusion is that according to the researcher, it fails to account for any changes in the number of accidents. More generally, his response was that traffic engineering's models for accident prediction is rough at best. Reading between the lines, his response was more along the lines of accident prediction models are "pretty darn bad." In my casual reading of traffic engineering articles and books, there seems to be a line of thought that aggressive driving is a major cause of accidents. Well, people are going to have these runways to zip ahead -- over one mile in heavy traffic! -- in an attempt to cut in line. However, my experience is that people cutting in line tends to irritate others resulting in more aggression in return. My take is that omitting these accidents from the simulations creates a downward bias in the travel times that would bias any comparison made when choosing projects in the first place. Moreover, it also opens up the possibility that even if the project results in a net decrease in average travel times, it might increase the empirical variance of travel times since an accident can create a real travel quagmire. In other words, the projects might make an ordinary day a little better but make it more likely that a commuter gets stuck in a nightmare. Whether that would represent an improvement is dependent on preferences but would be a turn for the worse in by my standards. Let's remember that people do get hurt in accidents. What the tradeoff is between travel time and personal injury is unclear to me. That travel times could get worse and we have more people getting hurt is obscene in my opinion.

At least based on intuition, I have less objection to project #2. That is, I can see how it decreases travel times. I guess it might help with traffic closer to the District by relieving later bottlenecks; although I suspect not. Whether it is worth the money and impact on residents nearby I-66 is another issue and others have written extensively on it. I have little to add other than it is my opinion that you should ensure that the plan is aesthetically and environmentally acceptable to a majority of those affected. At the moment, it is unclear whether VDOT has satisfactorily addressed local concerns.

My last point is that I am a believer in, "If you build it, they will overuse it." That is, if by chance the engineering changes represents an improvement in travel times, a subset of people using an alternative will substitute away from their present choice and drive. Or alternatively people will recognize the improvements and be more likely to reside/work in a location that takes advantage of this new improvement. This will occur until no advantage exists relative to any other alternative. I find it hard to believe that these projects are really addressing the big issue in a meaningful way. I would rather that my tax dollars be better used on something that truly represents -- or at least something that we have a high degree of confidence -- an improvement in a time where state and federal governments need to be more conscious of its dollars.

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