Key to cutting infrastructure costs: TND
Infrastructure costs are 32 to 47 percent lower in traditional neighborhood development (TND) than in conventional suburban development, according to a study recently completed by Jonathan Ford of Morris Beacon Design.
The study, “Smart Growth & Conventional Suburban Development,” looked at alternative ways of developing the 750-acre “Belle Hall” site in Mount Pleasant, South Carolina, and the 575-acre Dove Valley Ranch north of Phoenix. It found that the compact, interconnected grid associated with TND allowed “more appropriate pavement widths and a greater variety of street types” than were possible in a conventional development organized around collector streets and cul-de-sacs.
Among the points that Ford makes about infrastructure costs are these:
• A conventional development layout “funnels traffic to a small number of collectors and arterials, which typically require additional lanes to accommodate much higher demand.”
• Streets in a conventional suburban development are often required to be wider than in a TND “because they serve as the only route for emergency responders.”
• A sizable portion of parking demand in a TND can be accommodated on the thoroughfares, eliminating some of the need for paved off-street parking. The mixing of uses and the compact urban form associated with a TND also help to reduce parking demand. A TND may get by with as much as 40 to 60 percent less parking than a conventional development.
Ford acknowledges that the total length of streets and alleys may be greater in a TND than in a conventional development (where most often there are no alleys). However, he says the alleys in a TND are “essentially balanced” by the driveways in a conventional development.
Savings from density
The study suggests that the total cost of streets and parking per residential unit in a TND is 30 to 46 percent less than that of a conventional development. To a large extent, this reflects the higher density achievable in a TND.
Also of interest, given the environmental costs of stormwater runoff, is Ford’s finding that various TND scenarios result in 42 percent less impervious area per housing unit when compared to conventional development.
Material in the report is adapted from “Comparative Infrastructure & Material Analysis,” a study in which Ford was engaged for the US Environmental Protection Agency. The material appears in an EPA working publication called “Smart Growth: The Business Opportunity for Developers and Production Builders.” The new study can be downloaded at www.morrisbeacon.com.