No Time to Detour from Viable Transportation Solutions

November 10th, 2006 by Leave a Comment

By Benita M. Dodd

Traffic congestion in metro Atlanta, where half the vehicle miles traveled in Georgia are concentrated, is frequently blamed on land use patterns in a region derided as the poster child for sprawl. But just how much would it help for transportation agencies to focus on “smart growth” initiatives like transit-oriented, mixed-use, in-fill and higher-density development?

Not much, according to Alain Bertaud, an urban planner with more than 30 years’ international professional experience. In fact, he maintains that “as long as voters believe that federally subsidized transit and smart growth will solve the congestion and pollution problems they are unlikely to support solutions which address the problems.”

Bertaud, who has used geographic information systems (GIS) extensively to examine the spatial structure of urban areas around the world, calculates the average population density by dividing total population by built-up area rather than by administrative area. He also looks at the density profile, which shows whether the city center is a strong draw for jobs or whether people and jobs tend to be distributed across a metro area.

In his 2002 study, “Clearing the air in Atlanta: Transit and smart growth or conventional economics,” Bertaud concludes that Atlanta’s average density is six people per hectare, which equates to 1,554 per square mile. (The Census Bureau’s 2000 calculation puts the Atlanta metropolitan statistical area density at 671.5 residents per square mile.) As for Atlanta’s density profile, he calculates that the population density within a half-mile of the city center is 12 times lower than within the same distance in Paris. There’s also little difference between density in the city center and the suburbs, suggesting that the city center is a weak attractor of jobs and population. In fact, Bertaud notes that metro Atlanta’s spatial structure of extremely low density and an extreme dispersion of jobs and people “is not only exceptional among world cities but also among U.S. cities.”

“Does it matter? If one looks at economic viability, Atlanta’s success suggests that the answer is obviously no,” Bertaud notes. “But urban structure matters when designing a strategy that rests on the development of transit as a major mode of transportation.”

If you consider Atlanta’s low density, he concludes, it’s not surprising that the region finds it difficult to develop a transit system that is convenient for the commuter and financially viable for the operator. A higher density also doesn‘t guarantee a high share of transit. Dispersion of jobs and people are just as important. Operating transit lines with multiple origins but one destination – the city center – is easier than operating transit with multiple origins and multiple destinations. Routes have fewer passengers when jobs are more dispersed.

Efforts to change Atlanta’s spatial structure require stimulating drastic increase in density, jobs and amenities in the city center, Bertaud says. Using increased transit frequency and routes, or drastically regulating land use, according to Bertaud, can get 60 percent of Atlantans within a third of a mile of a transit stop. But that measure, which in similarly populated Barcelona, produced 30 percent transit ridership – would require about 2,800 new stations for metro Atlanta.  

How drastic would land use regulation need to be? For Atlanta to reach the “viable” threshold for transit would require a population density in the built-up area that is five times higher than it is now, Bertaud estimates – about 7,770 people per square mile. Even considering the region’s population growth rate, achieving that threshold would require about two-thirds of the existing real estate stock to be destroyed over 20 years; two thirds of the built-up area would have to revert to nature, and population and jobs would have to move into the 36 percent of the city remaining. 

Transit proximity has not been a major consideration for business or new housing development in the metro area, but traffic congestion has been a dissuading factor and a constant complaint. Georgia ties with Florida at 23rd in the nation for the solo commute rate: 80 percent of Georgia commuters travel to work alone. Census projections put Georgia’s population at 12 million by 2030, with half those residents making the metro area home.

Traffic will increase in metro Atlanta; and according to a study published by the Transportation Research Board in October, suburb-to-suburb accounted for a 46 percent of share metropolitan commuting, while suburbs saw more than 61 percent of the nation’s growth in jobs. That study also saw jobs in suburbs increasing and jobs in central cities declining, and more workers are making “trip chains,” meaning more stops during their trips to and from work.

What Bertaud’s study makes clear is that while transit has a role to play, the role is nowhere near significant enough to put a dent in traffic congestion in metro Atlanta. Creatively adding capacity in Atlanta is one way to reduce congestion while respecting commuter choice. That includes adding highway lane miles and improving arterial roads – a commitment to road construction. Guiding commuters to consider the value of their trip and time is another way. Implementing toll roads, for example, using dynamic prices based on the level of congestion or time of day, would promote carpooling and reduce rush-hour recurring bottlenecks, which comprise 48 percent of congestion in metro Atlanta.

Congestion need not be a fact of life in metro Atlanta. Governments need not restrict the lifestyle choices of their residents to reduce congestion. So why the persistence of transit-based solutions? Bertaud explains it succintly: “Making people pay for something which was previously free, and correspondingly overused, is difficult to sell politically. It is easier to sell the idea of increasing federal transfers to expand a transit system. The reduction of congestion in Atlanta is therefore a political problem much more than it is a technical one.”

To access the study, visit


Benita M. Dodd is vice president of the Georgia Public Policy Foundation, an independent think tank that proposes practical, market-oriented approaches to public policy to improve the lives of Georgians. Nothing written here is to be construed as necessarily reflecting the views of the Georgia Public Policy Foundation or as an attempt to aid or hinder the passage of any bill before the U.S. Congress or the Georgia Legislature.

© Georgia Public Policy Foundation (November 10, 2006). Permission to reprint in whole or in part is hereby granted, provided the author and her affiliations are cited.

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