To the Editor: Demand, Braess’ Paradox and Roads

Building more roads will not necessarily ease traffic; we need a comprehensive look at our transportation options going forward.

Now that the Virginia Supreme Court has weighed in on the Greenway, we have started to hear more on “alternatives” that include extending old roads and adding lanes to others. The truth is that these fixes may or may not reduce traffic in the short term, and probably will not in the long term, and may even make matters worse.

This may seem counter intuitive – that more driving options could lead to more traffic – but the idea is out there and has been proven to exist, especially in growing metropolitan areas. There are two ideas at play here. One is called induced demand, which is that idea that creating more of something also creates new demand for something. The other is called Braess’ Paradox, which shows mathematically how it works, predicting that removing some roads entirely actually reduced traffic in extreme cases. These work together to either encourage new drivers (or drivers who would otherwise be using another form of transportation) to get on the road, and encourage more people to (quite literally) cut corners in the same way, at the same time, only to get stuck in a different place.

I should be clear as to what I am arguing for in this letter, however. I am not suggesting that the road improvements are not needed where they have been proposed. I cannot personally speak to that. I am saying that this, or some form of success as it pertains to the Greenway (be it reduced rates or acquisition), should not be considered grand solutions to the problem of traffic congestion. They simply cannot be because it is a more complicated (and often regional) problem than a lack of roads.

As an aside, we do know what the solution to traffic congestion is: get more cars off the road. More roads can work, as long as they are accompanied by a comprehensive set of choices: public transportation, car-pooling, building more densely to provide walkable and bike-friendly options, and yes, even tolls reduce traffic. Remember: the idea behind privatizing the Greenway in the first place was to create less-trafficked option based on letting the company run it as a business, not a public good.

In summary, I do not believe the recently proposed road expansion efforts (or any iteration of using the Greenway) will improve the Northern Virginia (not just Loudoun) traffic situation, nor do I believe it will cause any noticeable harm. I simply think that all modes of transportation need to be considered for County investment if we hope to make a real impact on the situation.

Truman Horwitz


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