Pushing Sprawl Through Flawed Congestion Analysis

One crucial distinction in regional planning is between approaches to commuting that simply look at moving people as far as possible as fast as possible and approaches that look instead at moving people from where they are to where they’re going as fast as possible. For example, consider the Texas Transportation Institute’s new report on congestion in America which lists DC as tied for first for hours wasted in traffic, in the context of how their methodology actually works:

The TTI report narrowly looks at only one factor: how fast traffic moves. Consider two hypothetical cities. In Denseopolis, people live within 2 miles of work on average, but the roads are fairly clogged and drivers can only go about 20 miles per hour. However, it only takes an average of 6 minutes to get to work, which isn’t bad.

On the other hand, in Sprawlville, people live about 30 miles from work on average, but there are lots and lots of fast-moving freeways, so people can drive 60 mph. That means it takes 30 minutes to get to work.

Which city is more congested? By TTI’s methods, it’s Denseopolis. But it’s the people of Sprawlville who spend more time commuting, and thus have less time to be with their families and for recreation.

The point is that if you simply want people to be inside fast-moving vehicles, that will always bias policy toward sprawl. If you make each house sit on a large enough lot and build reasonable wide roads, then traffic will always move very quickly. But it will move quickly in part because everything’s so far away. Living in downtown DC where things are very close together, it’s most practical for me to commute to work via the incredibly slow method of walking. But I love only 0.8 miles from my office, so the trip only takes 10-15 minutes and by any sensible estimation it’s a very pleasant and convenient commute.