By Jerry Walters

Several new reports on the subject of transportation, land use and climate interactions, reach findings related to and/or directly refer to the findings of Growing Cooler- The Evidence on Urban Development and Climate Change, a 2008 ULI book co-authored by Fehr & Peers. This second of three posts will clarify the misconceptions and key differences between Growing Cooler and the most prominent of these studies:

• Last week: Moving Cooler – by Cambridge Systematics for ULI, EPA, US DOT, et al
• This week: Driving and the Built Environment – by a group of academics and national experts for TRB and the National Research Council.
• Next week: Travel Behavior, Residential Preference, and Urban Design – by the University of North Carolina

Driving and the Built Environment

This National Research Council (NRC) report finds lower VMT reduction resulting from land use strategies than did Growing Cooler and than were adopted into Moving Cooler. It estimates that the potential reductions in inter-urban passenger travel resulting from land use shifts and complementary transportation would be in the range of no greater than 8 to 11 percent by 2050, while Growing Cooler estimates the likely range to be between 12 and 18 percent.

The authors of Growing Cooler believe that the lower NRC estimate is the result of several questionable assumptions:

· The NRC study does not take into consideration the effects of more compact future commercial development and redevelopment, it only examines density increases related to residential growth,

· NRC assumes very, very slow redevelopment of residential properties, equivalent to about 500-year life-cycle for housing stock, compared to 170-year life-cycle projections that informed other studies such as Growing Cooler,

· The NRC analysis considered the effects of development density on VMT reductions but not the additional 4D effects of diversity (mixed use), design (walkability and connectively), destination accessibility (infill vs. spread sites), and development distance to core transit,

· The NRC study does not consider the synergistic effects that infill and mixed-use development has on its neighboring land uses, which can occur if it fills needs for complementary land use types. This may result from adding services and entertainment to homogeneous residential areas, or adding housing near pre-existing jobs or retail, or adding a more connected and amenable pedestrian environment to what may have previously been a gray-field or brownfield. It may also result from creating critical mass that generates additional transit investment in the area,

· Also, by working with national averages, the NRC study uses very broad averages of development form, unlikely to register on the benefits derived at a neighborhood or community scale. As reported the study works with average existing residential densities of only 1.7 to 2.9 dwelling units per acre, and then assumes that new development will only occur at densities of 1 DU per acre. As a result, their estimates of VMT reductions have little in common with the types of reductions likely to correspond with the local effects of compact, mixed use development on the vast amount of travel that takes place within neighborhoods and within communities.

In conclusion, the Growing Cooler authors believe that their own estimates represent a fully achievable estimate of VMT and GHG reduction.

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Coming up next…

- I will review UNC’s Travel Behavior, Residential Preference, and Urban Design: A Multi-Disciplinary National Analysis, which states: “We found that residents of neo-traditional developments make more car trips … than residents of typical suburban neighborhoods… We found no difference in vehicle mileage.”