A recent study of North Carolina census data concludes that economic and quality-of-life factors have a much stronger influence on growth and "sprawl" than placement of roads does. The study, by University of North Carolina Prof. David Hartgen, "concludes that road projects are blunt and inefficient instruments for either spurring or slowing growth, so local governments should accept responsibilities for growth policies."
The study, titled Highways and Sprawl in North Carolina, reviewed the growth of North Carolina's 1551 census tracts during the 1990s in conjunction with locations of major road improvements. Hartgen used the data to determine the relationship between road investments and growth for each of 12 commuting regions.
The study states that local growth patterns depend heavily on prior density: growth goes where there is room for it, filling in the urban tracts and lower-density edge-of-city tracts. Local zoning limits on population within tracts thus push additional growth to the region's edges. Hartgen notes that about half the state's population growth went into tracts that had no major road improvements during the 1990s, and proximity to the interstate system or to city centers was not a factor in most regions.
Hartgen further concluded that recent major road improvements--mostly road widenings--had a minor effect on growth, increasing it by 50-550 persons per decade, per mile of investment, about 2-14 percentage points above the baseline growth. However, the relationships varied widely by region and were weak. Hartgen concluded that factors other than density or road investment--such as schools, taxes and availability of sewer and water service--significantly influence the location of growth, but that road projects are not as strong a factor.