Ask CNU: Low-traffic New Urbanism

Today in Ask CNU, Sue from Durango asks, "has anyone quantified the impact that New Urbanism can have on reducing traffic around me?"

It's rare -- but possible -- for new development to actually reduce the amount of traffic on the streets surrounding it; after all, it is still new development. However, New Urbanism (and in particular mixed uses, higher densities, and higher street connectivity) has potential as another tool in a full transportation demand management toolkit that can reduce the number and distance of car trips made. TDM is hard for many transportation planners to understand because its principles often seem counterintuitive -- and, indeed, it is an entirely different way of thinking about transportation.

The best single source of information on TDM is the Victoria Transportation Policy Institute's exhaustive TDM Encyclopedia.

Adam Millard-Ball and Patrick Siegman, CNU members at Nelson\Nygaard in California, have developed a "mitigation component" for air quality modeling software that accounts for the reduced number of trips created by well-located, well-designed developments. This can help to provide more realistic trip generation numbers than the stock answers supplied by blindly (and incorrectly, they note) applying ITE Trip Generation figures to all new developments. It's an interesting paper, and a good start in a field (traffic modeling) that many CNUers believes is a good candidate for New Urbanist reform.

A few cities, notably Boulder, London, Lyon, and Vancouver, B.C., have reported successes in actually reducing the number of car trips within their central areas while still accommodating growth. Their strategies have varied quite substantially, but are worth taking a look at as cities seek ways to both reduce pollution and improve quality of life.

Ask CNU is an occasional column where Payton Chung, CNU's Research Coordinator, answers your questions about New Urbanism. Submit your questions to me at pchung{at}


Effects of TODs on Housing, Parking, and Travel

A recent study of Transit Oriented Developments and its effects, completed by PB Placemaking, Dr. Robert Cervero, the Urban Land Institute, and the Center for Transit Oriented Development, confirms what many people already believed: TODs reduce traffic. As the Executive Summary of the study explains, "this research helps confirm what had been intuitively obvious: in the four metropolitan areas studied, TOD-housing produced considerably less traffic than is generated by conventional development."

The study compared car use for 17 different TODs in Portland OR, Washington D.C., San Francisco Bay Area, and Philadelphia/Newark. The results confirmed that the estimations used by the Institute of Transportation Engineers (ITE) to determine car-use around TODs were grossly overestimated. For peak A.M. hours, Washington was 59.9% below ITE estimations, Portland was 49.6% below, and San Francisco Bay was 47.5% below. The Philadelphia/Newark area, which receives limited rail service, was 30.53% below ITE estimations.

The report is expected to be available in October through the Transit Cooperative Research Program.

To check out more on the Transit Cooperative Research Program.

PB Placemaking's website


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