Pedestrian cities were dense, compact and likely walled.

Sprawl

What Happened?

In the second half of the 20th Century, the spreading out of urban activities into outlying suburbs raised issues mainly of aesthetics and loss of farmlands and forests. Sprawl was criticized as wasteful and ugly. Today concerns for the use of gasoline by fleets of all kinds of road vehicles and beyond that travel longer and longer distances through ever-enlarging metropolitan regions have taken center stage in the debate over sprawl.

When a city sprawls, its various parts – housing, retail, offices, and other cultural and recreational facilities – spread out at distances that make for long trips on a regular basis. The statistics of per-capita trip-making and VMT – vehicle-miles traveled -- have risen steadily. Here is a clear example that not all growth is positive.

Historically cities were scaled to pedestrian dimensions. Most mobility was by foot, so a one-kilometer distance was substantial. Most people moved less than 5 kilometers a week. Densities were high, and living was compact. Only the largest of cities spread out more than a five-kilometer radius.

Railroads enlarged that radius, with new suburbs developed compactly around stations. The coming of the automobile liberated people and businesses to locate at greater distances into areas of lower densities. The need for highways and parking to accommodate all the vehicles erupted into massive concrete and asphalt projects. Metropolitan regions now operate with radii of 30 kilometers or more, less centered on the traditional downtown district. Modern life is instead pulled in many different directions and many people travel 50 kilometers over the course of a typical day.

Cluster development reduces the sprawl and preserves green space.

Today’s urban growth is mostly now drawn by proximity to interchanges of major highways, such as the 80,000-kilometer Interstate network in the U.S. Each exit defines a development district with a radius comparable to the 2-3 kilometers. In the U.S., we have indeed sprawled. We have become an asphalt nation of increasingly obese people who drive rather than enjoying the benefits of healthful walking as a part of everyday life. Connected Variables With energy costs rising and concern for global warming surging, sprawl is taking on strong economic and ecological dimensions. It is clear that there is an indirect relationship between sprawl and urban density. The more we sprawl, the lower our settlement densities. In between these two variables is the mode split – the percentage of travel accomplished by cars versus transit, walking and biking. Tools How do we prevent sprawl? There are two sets of tools. Some serve as “carrots” to entice in-fill construction in dense, central locations. Other land use planning tools are like “sticks” that try to prevent development in outlying districts sprawled along highways. Growth boundaries have been used in Europe and, with some success, in Portland, Oregon. It is better to entice with positive incentives. APMs can offer easy, comfortable access in car-restrained districts of density.

Planning can encourage compact development and prevent sprawl.

Density patterns are the result of many factors.