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Rethinking Traffic Congestion
Traffic Expands to Fill Available Road Space

by Tom Samuels

North America is inundated with roads. Typically, 30 to 50 percent of the land area of cities and towns consists of infrastructure catering predominantly to cars and trucks.

This includes roads, right-of-ways, bridges, garages and parking lots.1 The highway system in the United States, for example, covers a land mass equivalent to the entire state of Georgia.2

Despite this, as well as an ever-increasing expansion of its road system, North Americans as a society are becoming less mobile than ever. People spend more and more time behind the wheel, caught in what appears to be an endless sea of traffic jams.3

Traffic congestion is now a fact of everyday life for most North Americans. The U.S. General Accounting Office estimates that traffic congestion costs the country over $100 billion a year in lost productivity alone.4 In Ontario, Canada, the figure is over $2 billion.5

Traditional attempts at congestion mitigation have followed a pathological paradigm whereby new and upgraded roads are built to meet forecasted future traffic demands. This "predict and provide" scenario has invariably led to the generation of new traffic and hence further congestion. Governments are stuck in a vicious cycle of trying to "build their way out of congestion."

Already in 1957, the respected urbanist Lewis Mumford called for a two-year moratorium on the construction of the multi-billion-dollar Interstate Highway System. Mumford warned that the Interstate (built, in part, for "national defense") "...will, eventually, wipe out the very area of freedom that the private motorcar promised to retain for them."6

The case of the missing traffic
In the mid-1960s, residents of New York City's Greenwich Village were confronted with plans to build a major highway through Washington Square Park. Transportation professionals were convinced that unless the highway was built, the projected traffic
demands of a proposed adjacent development would result in a traffic nightmare.

After a long and bitter battle, the residents succeeded not only in stopping the highway, but also in permanently closing an existing road. The prophecy of doom and gloom never occurred. The predicted additional traffic volumes were never generated.7

Robert Morris, in a 1977 article titled "Traffic as a Function of Supply and Demand," conducts an investigation into the whereabouts of this "missing" traffic.8 Morris examines the relationship between the capacity of a road system and the demand for the use of that system. His case study is U.S. Route 1, an arterial road that runs through Arlington, Va., linking the Pentagon with Alexandria, and passing Washington, DC's National Airport.

Morris found that between 1961 and 1973 more than 5.3 million square feet of office space, 2,720 apartments and 996 motel units were built adjacent to U.S. Route 1, to create the concrete jungle now known as Crystal City. Transportation planners forecasted that daily traffic volumes would exceed 77,000 vehicles, which was deemed to be far beyond the existing road's capacity. Despite recommendations to widen the road, and to have grade separations at intersections, the development went ahead without the road improvements.

In 1975, U.S. Route 1 carried 34,400 vehiclesóless than half the predicted 77,000óat an "acceptable" level of service.

It's in the curves, Watson!
Morris takes readers of his 1977 article back to a first-year university economics class to answer the question, "Where did the missing traffic go?":

The basic rule of supply and demand as it relates to costs and quantity is that the number of widgets a person will buy depends on the price of the widgets. When the price is lowered, the number of sales increases; when the price is raised, the number of sales decreases. Supply works in a similar fashion in that the higher price Acme Widget Inc. can get for their product, the more widgets they are willing to produce. As prices drop, production is cut back; as prices rise, production increases.

The point at which the demand and supply curves cross is referred to as the "point of equilibrium." Here, supply and demand join harmoniously, establishing a balanced price and corresponding quantity for production. As conditions change (as is their wont), the demand and supply curves are redrawn, thus establishing new points of equilibrium.

Back to transportation: The "demand" in this case is trip generation. The "supply" is the available transportation system. Consumption is the number of trips taken, and is a function of the costs of those trips, typically measured in the time it takes. Thus, when cost (time) is increased, fewer trips are taken (demand); when costs are decreased, more trips are taken. [See article on previous page.]

For example, if in response to a congested road, new lanes are added, travel speed will increase, trip time will decrease and trips taken will increase. If, on the other hand, in response to a congested road, nothing is done, or lanes are removed, then trip time will increase, and demand and consumption will both be reduced.

Transportation planners themselves have a plethora of research that comes to this very same conclusion. Referred to as the Pigou-Knight-Downs paradox, or the Downs-Thomson paradox, or even the Braess paradox, the general conclusion is that expanding a road system as a remedy to congestion is not only ineffective, but often counterproductive.9

Transportation expert Stephen Plowden made this point accessible to those of us with phobias for complex mathematical charts:

"Very broadly speaking, the amount of traffic is governed by what is regarded as a tolerable level of congestion. If the capacity of the road network is increased, whether by road construction or traffic management measurements, the mileage will increase until the same conditions obtain. If the capacity of the road network is not increased, the mileage performed will stabilize, and if the capacity is reduced, the mileage will be reduced correspondingly."10

The First Step
The best solution to effect an immediate improvement to our transportation system is to encourage congestion. Much of North America's "congestion crisis" is comprised of discretionary traffic, which in turn is generated because of readily available and extensive road systems. For example, an estimated 40 percent of the car trips on U.S. interstate highways during peak hours are non-work related.11 Thus, by reducing the capacity capability of our road system, less "latent demand" is actualized in the form of new car trips as drivers are forced to reconsider their travel habits.

The Greater Vancouver Regional District recently adopted this philosophy in its Long-Range Transportation Plan, which states: "Selectively accepting congestion to change travel patterns is another (transport service) policy lever...Congestion is usually considered an evil; however, allowing congestion to deteriorate for the single-occupant vehicles is a practical method of promoting transit and carpools."12

Practically, we need an immediate halt to the expansion of the road system. Wherever possible, existing road space should be reclaimed from cars and trucks. With the "freed-up" road spaceóand resourcesóa wealth of creative and alternative transportation measures are made possible, including bicycle lanes, pedestrian paths, dedicated transit ways, landscaping and traffic calming.

By better understanding the link between road building and trip generation, transportation decision makers can seriously challenge this key ingredient that
maintains our car-dominated society.

A paving moratorium offers decision makers a way to incorporate the above-stated ideas and concepts into our individual and societal mindsets. However, logical and well-thought-out arguments, in and of themselves, are not sufficient to create social change. Transportation planners, government officials, academics and citizens have been well aware of the impossibility of "building one's way out of congestion." Yet our governments continue to build and widen roads. Change will occur only if a critical mass of vocal and dedicated citizens is developed.

Begin by talking about this with your friends and neighbors. Further educate yourselves on this topic, especially in terms of creative and sustainable alternatives to building and widening roads. Start to lobby your local politicians for change. Launch a campaign against any road building or widening program in your community.

Tom Samuels is an activist with Toronto's Better Transportation Coalition. Feel free to contact him there: BTC, 736 Euclid Ave., Toronto, Ontario M6G 2V2, Canada; (416) 536-6568;

1. Smith, Malcolm. State of the Environment Fact Sheet: Environmental implications of the automobile. SOE Fact Sheet No. 93-1. Ottawa: Environment Canada. 1993. p. 4.

2. Goddard, Stephen. Getting There: The epic struggle between road and rail in the American Century. Harper Collins: New York. 1994. p. 253.

3. Citizens Advocating Responsible Transportation. Traffic Calming: The Solution to Urban Traffic and a New Vision for Neighborhood Livability. Oregon: Sensible Transportation Options for People. 1993. p. 13.

4. Goddard. 1994. p. 254.

5. Ontario Ministry of Transportation. June 1994. Highway 407 Information Brochure II. Ontario, Canada.

6. Goddard. 1994. p. 253.

7. Plowden, Stephen. Towns against Traffic. London: Andre Deutsch. 1972. p. 117.

8. Morris, Robert. "Traffic as a Function of Supply and Demand." In Traffic Quarterly. Volume 31. Connecticut: ENO Foundation for Transportation. 1977. pp. 591-603.

9. Arnott, Richard and Kenneth Small. "The Economics of Traffic Congestion." In American Scientist. Volume 82. North Carolina Scientific Research Society. (Sept.-Oct. 1994). pp. 446-455.

10. Plowden. 1972. p. 15.

11. Cameron, Michael. Transportation Efficiency: Tackling Southern California's Air Pollution and Congestion. Washington, D.C.: Environmental Defense Fund. March 1991.

12. Transport 2021. A Long-Range Transportation Plan for Greater Vancouver. Vancouver: Greater Vancouver Regional Dist./Province of British Columbia. 1993. pp. vi-ix.

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