Sunday, February 12, 2012

How Not to Manage Urban Traffic Congestion

I once listened to the Achim Steiner, Executive Director of the United Nations Environment Program, recount his exasperation with Nairobi traffic. On that morning it had taken Achim Steiner over two hours to drive 10.8 kilometers, the distance between his office and Kenyatta International Conference Centre.

You would think the solution to Nairobi’s traffic congestion is simple: build new roads; widen existing roads; construct fly-overs and elevated expressways. Planners think of roads as neat and logical solutions to traffic congestion. Politicians see roads as populist legacy projects. Consultants and contractors view roads as cash vendors. For lenders, it’s shovels of money out the door. And people, both urban and rural, find roads sexy.

The unvarnished truth is that building new highways, however fancy, or widening existing roads does nothing to reduce traffic congestion. On the contrary, increasing road supply invariably increases vehicle traffic. This is paradoxical and merits repeating: expanding urban roads makes traffic congestion worse, not better.

In 1942 Robert Moses, master builder of mid 20th century New York City observed that the highways he built around New York in 1939 were somehow generating greater traffic congestion than had had existed previously. Since Robert Moses’ intuitive observation, the relationship between roads supply and traffic congestion has been has elicited robust scholarship.

A study of interstate highways and vehicle kilometers traveled in US cities showed that increased supply of highways did not ease congestion in the absence of congestion pricing. Similarly, the Southern California Association of Governments noted that expanding highway capacity would have no more than a cosmetic effect on Los Angeles traffic. The best solution, the association concluded, was to advise people to work closer to home.

In the short term, increased highway capacity makes longer commutes less irritable, and as a result, more people are willing to live farther from their workplace. As more people make similar decisions, the once pleasurable long commute gets crowded and the clamor for additional lanes starts again.

A recent study by University of California at Berkeley found that for every 10 percent increase in highway capacity, vehicle traffic increased by 9 percent within a period of four years. Trying to end traffic congestion by adding more capacity is like trying to reduce your girth by loosening your belt. In my mind, the question is not how many lanes must be built to ease congestion but how many more lanes of congestion do we want, three or eight?

Urban transportation experts have argued that the real constraint to driving is traffic congestion, not cost. There is a predominant notion that there is such a thing as latent demand for lanes. Because of latent demand, adding more lanes is futile because commuters are waiting to snap them up as soon as they are built. Some urban transportation scholars have argued that latent could be as high as 30 percent for most cities.

The Kibaki administration has embarked on highway expansion of unprecedented scale. Thika road is currently undergoing major expansion into a 50.4-kilometer eight-lane superhighway at an estimated cost of KES. 27 billion ($330 million). However, the consequence is unsettling. Almost all of the billions of shillings spent on road expansion will have accomplished only one thing, which is to increase the amount of time that you must spend in your car each day.

Effectively managing Nairobi’s congestion requires both a holistic and integrated approach, which goes beyond contemporaneous congestion and extends to the management of the urban space as complex system. Congestion mitigation actions must include a broad and comprehensive land use, urban planning, investment in public transportation and general transport master planning process.

Highway expansion must not be seen as a panacea for Nairobi’s irksome traffic congestion. If it is, then the engineers are wasting their time and the government is wasting our money on an expensive stopgap measure that will produce only temporary relief.

Currently, road access in Nairobi is unconstrained by anything but traffic congestion. How might measures besides expensive highway expansion be deployed to congestion management?

I suggest two measures. The first is parking management. Control and management of parking can be used to modify demand on an area-wide basis to manage traffic congestion. Metered parking control can be targeted on the basis of location and time.

The second is congestion pricing. Congestion pricing is a way of using the power of the market to reduce congestion. Congestion pricing would work by shifting discretionary rush hour highway private traffic to public transport or to off-peak periods. There is a consensus among economists that congestion pricing represents the single most viable and sustainable approach to reducing traffic congestion.

Eradicating traffic congestion solely through highway expansion is neither an affordable, nor feasible goal in economically dynamic city like Nairobi.

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