Measuring Sprawl in the Washington Metropolitan Region

"Sprawl" is a difficult concept to define and encompasses many different economic, social and environmental issues. One aspect of sprawl has to do with the distance of new development from existing or planned services, such as roads, sewer systems, schools, etc. Infrastructure development to provide these services is much more costly if new development is dispersed or occurs far from existing or planned services. Using the Masek and Lindsey data set, simple measurements can be performed that illustrate regional differences in patterns of development. The Washington, D.C. Metro system provides a simple example of a service that can be used to indicate sprawl patterns since plans for the Metro were finalized by the late 1960's. Planners and local governments in the Washington metro area would have been aware of future Metro service and therefore had the opportunity to plan growth accordingly.

Montgomery County, Maryland and Fairfax County, Virginia were compared in this analysis. The distance of new development to the nearest Metro stop was calculated for each time period in the Masek and Lindsey data set.

New growth between 1973-1985 is shown in green, 1985-1990 is shown in orange, and 1990-1996 is shown in red. Only metro stops in or near Montgomery and Fairfax counties were included and are indicated by colored circles.

This calculation produced a summation of the area of new development occurring within a certain distance of a Metro stop. Raw area totals were normalized by the total county area to account for size differences between Montgomery and Fairfax counties and then placed into eight categories based on distance. The results are summarized by these histograms:

The contrasts between sprawl patterns in Montgomery and Fairfax counties are striking. Montgomery County has consistently developed closer to the Metro system than Fairfax County between 1973 and 1990. Both counties exhibit similar trends between 1990-1996, when most development occurred within 13 kilometers from a Metro stop. Montgomery County seems to be spreading out, as shown by the fact that almost 10% of new development between 1990-1996 occurred between 23 and 30 kilometers while Fairfax County did not have any new development over 23 kilometers away from the Metro.

Another piece of information that can be extracted from the Masek and Lindsey data is the rate of development. The square kilometers of development per year was calculated, and again we see striking differences between Montgomery and Fairfax counties:

The rates of land conversion were consistently lower in Montgomery County than in Fairfax County, especially between 1985-1990. This time period represents the maximum rate of land conversion for both counties, but in Montgomery County the rate is 4.6 km/year while in Fairfax County the rate is 10 km/year.

This simple analysis produced some results that demonstrate the striking differences in development patterns between Montgomery and Fairfax counties. These different patterns produce different economic, social and environmental consequences. The cost of infrastructure development is likely higher in Fairfax County. Traffic congestion has become a serious problem for both counties, but the loss of open space is far more critical in Fairfax County. These types of problems impact the quality of life of county residents, and can also contribute to serious environmental problems, such as compromised water quality. Both counties have attempted to institute growth control measures and conservation programs, but Montgomery County has met with more success. The results of this analysis reflect the differences in planning and conservation strategies between the two counties.