The future of traffic congestion

I just wrote this for the Move Forward blog:

Recent statistics from the Texas A&M Transportation Institute suggest congestion is rising. A congested city, compared to exactly the same city where everyone can move faster, has lower accessibility (the number of places travelers can reach in a given time is reduced). This limits people’s ability to interact, and thus reduces economic activity, but congestion is also a signifier of economic activity. All the great cities are congested.

We would have much less congestion in New York if we closed all the bridges and tunnels entering Manhattan, as all those trips would no longer be made. However that would be a net negative from an accessibility perspective. So, how congestion is addressed matters.

Short term volatility in congestion levels is to be expected. In the very short term, with low unemployment and low gas prices, traffic rises, and as gas prices and unemployment eventually rise again, traffic diminishes.

Over the longer term, there is only so much travel individuals want to or can make; there is only so much time in the day. In contrast with the short-term spike, the mature economies have seen per capita travel largely falling over the past decade or two.

Continued population growth can offset that per capita decline, but that too is leveling off. New technologies are changing whether and how people travel, including telecommuting, e-shopping, and being virtually connected to your friends and family 24/7. Labor force participation continues to fall (even with economic expansion) as automation and information technology change the nature of work.

Overall this nets out to congestion being fairly flat over time (the US’s total vehicle travel in 2015 is at the same level as about 2007, despite a population about 7 percent larger). Reductions in traffic from one cause will induce people to make longer trips or more trips for another. In the absence of road pricing, and with current technologies, congestion levels will change slowly.

However, current technologies, with drivers behind the wheel, will not last. In particular, vehicle automation, once it gets critical mass, should greatly increase road capacity, both because of shorter following distances and because of narrower lanes. New, narrow vehicle forms designed for a single passenger (which is how most cars are used) will become more widespread with automation, as safety fears diminish, and will also increase person throughput.



Effective land use planning can increase accessibility, it can make cities more valuable, it can increase transit ridership, but in practice it won’t do anything significant for congestion. There are marginal things about where you locate driveways and such, but the main issue is that development density, which is good for transit, will increase rather than decrease congestion in its vicinity.

Allowing mixed uses will reduce some need for some travel, as people can do multiple things on-site, but the basic laws of travel demand are that more people, jobs, shops, restaurants, will generate more traffic locally than fewer people. Many city centers in Europe are banning the private car. So, there are now and will be more places that are free of traffic.

Mobility, the speed and directness of travel, and the density of activities are the two determinants of a city’s accessibility and thus economic vitality. Moving people faster, and more directly, in order to expand accessibility should be the primary mission of transport agencies.

Strategies to do that from the public policy sphere include pricing roads and reallocating street space to more productive uses. Cities are getting smarter about both. Furthermore, technological change with autonomous and smaller cars is moving in the right direction. The future is looking bright, and less congested.