Anthony Downs’ law of peak hour traffic congestion

In 1962, Anthony Downs put forward the fundamental law of peak hour congestion on urban commuter expressways: peak-hour traffic congestion rises to meet maximum capacity.

Larger bus and train networks and more cycleways are never the solution. Just as more highways leads to more congestion because more people would drive to work, with fewer people driving to work if they fit enough to ride on the new cycleways, other people will start driving to work, instead of taking public transport, go shopping or otherwise do their transit business to take up the freed-up place in the traffic jam because a few more people are riding their bikes. Traffic expands to meet the available road space.

No highway or public transit systems in the world can handle all those people who want to move simultaneously without overloading the systems’ capacity. So delays inevitably arise as all those people try to use the same roads and the same transit systems during the same periods.

Down’s law of peak hour congestion means that road will be as congested at before after any new investment in road capacity because fewer people are taking public transport or postponing their trips to outside the peak hour times. The same principle means more telecommuting or staggered work hours will not relieve peak-hour jam because other drivers will shift into these periods. More commercial driving in peak hours such as by trucks and delivery vans is an obvious response to more road capacity.

If that expressway’s capacity were doubled overnight, the next day’s traffic would flow rapidly because the same number of drivers would have twice as much road space.

But soon word would spread that this particular highway was no longer congested. Drivers who had once used that road before and after the peak hour to avoid congestion would shift back into the peak period. Other drivers who had been using alternative routes would shift onto this more convenient expressway. Even some commuters who had been using the subway or trains would start driving on this road during peak periods.

Within a short time, this triple convergence onto the expanded road during peak hours would make the road as congested as it was before its expansion.

Peak-hour congestion is inherent to how modern societies operate:

  • most people will work during the same hours each day thereby increasing society’s productivity, but this requires most workers and students to travel at the same times;
  • metropolitan growth is accompanied by rising prosperity,  so more households buy more cars, and roads become more congested; and
  • high volumes of traffic generated incidents and accidents.

Road capacity expansions and extensions to bus and train networks  do not reduce traffic congestion. Congestion pricing is the main candidate tool to curb traffic congestion successfully. Pending that unlikely outcome, this is what Downs suggests we live with congestion as the sole viable option:

If you can’t commute by transit, as most people can’t, get an air-conditioned vehicle with a stereo radio, books on tape, a hands-free telephone, a CD player and perhaps even a microwave oven, and commute with someone you really like. Then regard the time you spend stuck in traffic as part of your regular leisure time, and learn to enjoy it—especially since congestion here is less intense in the summer.

Don’t get your hopes up about congestion pricing because they do not attack the main form of traffic congestion, which is on highways, not in the inner cities:

Limited road-pricing schemes that have been adopted in Singapore, Norway, and London only affect congestion in crowded downtowns, which is not the kind of congestion on major arteries that most Americans experience.

In a cautionary note from Downs, that is a shot at the green movement and public transport activists, Down said:

Traffic congestion is not primarily a problem, but rather the solution to our basic mobility problem, which is that too many people want to move at the same times each day.

Why? Because efficient operation of both the economy and school systems requires that people work, go to school, and even run errands during about the same hours so they can interact with each other.

That basic requirement cannot be altered without crippling our economy and society. The same problem exists in every major metropolitan area in the world.

The reality is despite all the protestations of the Anti-science, anti-progress progressive left, most people drive in rush hours because they live in low-density areas that  buses, trains and cycleways cannot efficiently serve. Traffic congestion is the result of prosperity:

Peak-hour traffic congestion in almost all large and growing metropolitan regions around the world is here to stay. In fact, it is almost certain to get worse during at least the next few decades, mainly because of rising populations and wealth. This will be true no matter what public and private policies are adopted to combat congestion.

But this outcome should not be regarded as a mark of social failure or misguided policies. In fact, traffic congestion often results from economic prosperity and other types of success.

More importantly, privately owned cars are more comfortable, faster, more private, more convenient in trip timing, and more flexible for multiple tasks on one trip than any form of public transit. What cannot be avoided is:

As household incomes rise around the world, more and more people shift from slower, less expensive modes of movement to privately owned cars and trucks.

Downs argues that it is time to settle down and accept what cities are:

….peak-hour traffic congestion is inescapable in large modern metropolitan areas the world over. Business firms want most people on the job during the same hours so that workers can interact efficiently. Many firms also want to locate in low-density establishments scattered across the landscape.

Households want a range of choices of where to live and work, and most want to live in low-density settlements that are separate from poorer households, use private vehicles for most travel and be able to carry out multiple errands on a single trip.

I was surprised to learn that Anthony Downs was still alive. He wrote the Economic Theory of Democracy in 1957 and Inside Bureaucracy in 1967, but I just discovered that he was in his mid-twenties and 30s when he did that. Downs has gone on to be an excellent transport economist. A transport economist not enamoured with public transport, but instead with transport systems that suit the needs of real people with real lives.

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