Researchers analyzed the number of destinations that can be accessed within a given amount of travel time by mode (automobile and transit) and purpose (work and non-work trips) for about 30 US metropolitan areas. They found that although denser urban development tends to reduce vehicle travel speeds, the increased proximity is about ten times more influential than travel speed in determining a metropolitan area’s overall accessibility. This indicates that smart growth policies which increase development density and mix, transport network connectivity, and transport system diversity can do more to improve overall transport system performance than efforts to increase traffic speeds and reduce congestion.
The authors conclude, "Having destinations nearby, as when densities are high, offers benefits even when the associated congestion slows traffic. Where land use policy frequently seeks to support low-development densities in part in an attempt to maintain travel speeds and forestall traffic congestion, our findings suggest that compact development can often improve transportation outcomes."