What cities should do about traffic congestion

Many of the “remedies” for traffic congestion have ultimately made cities less livable. Expressways usually deaden the corridors they pass through. One-way street networks often become raceways — endangering pedestrians and harming retailers.

What should a city do instead? A chief answer, asserts an important new book by Jeffrey Tumlin, is “transportation demand management,” or TDM. In a chapter of Sustainable Transportation Planning: Tools for Creating Vibrant, Healthy, and Resilient Communities, Tumlin and two fellow transportation planners at Nelson\Nygaard Consulting Associates urge urban areas to learn from the successes achieved through TDM. TDM not only helps to alleviate congestion; it can also help create a more intact, walkable community.

TDM consists of strategies for making a transportation system more efficient, partly by reducing the number of single-occupant car trips and shifting some auto trips to times when the roads are less crowded. In their chapter on TDM, Tumlin, Jessica ter Schure, and Patrick Siegman — principals in Nelson\Nygaard’s San Francisco office — argue that TDM is crucial to effective transportation planning.

“TDM strategies are often far more cost-effective” than expanding road capacity, the three say. Frequently, TDM relieves congestion at little or no cost. “Short of major demand management techniques — particularly

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