The cul-de-sac is perhaps the quintessential symbol of suburban America. Perhaps millions of them have paved over greenways throughout the country. Hailed for their safety (no traffic that can run over kids) and prized by developers because they allow more houses to be built into oddly shaped tracts and right up to the edges of rivers and property lines, planners and town officials are beginning to realize their downside.<\/p>\n
Early last year the state of Virginia became the first state to severely limit cul-de-sacs<\/a> from future development. Similar actions have been taken in Portland Oregon, Austin, Texas, and Charlotte, North Carolina.<\/a> What they are beginning to realize is that the cul-de-sac street grid uses land inefficiently, discourages walking and biking, and causes an almost complete dependence on driving, with attendant pollution and energy use. Furthermore, town officials are beginning to realize that unconnected streets cost more money to provide services to and force traffic onto increasingly crowded arterial roads, which then, in many cases, need to be widened (more tax money).<\/p>\n <\/p>\n Two interesting studies were presented<\/a> at the CNU Transportation Summit in 2008<\/a> that examined the public safety and financial implications of street <\/span> <\/p>\n Twenty-four California cities were analyzed at the In addition to intersection density, the researchers also
\nconnectivity. They both seem to support what critics have begun to voice about the downside of cul-de-sacs grid networks. The first study was conducted by Norman Garrick and Wesley Marshall, of the University of Connecticut\u2019s Center for Transportation and Urban Planning. <\/a>Their study<\/a> investigated the relationships between connectivity, network configuration, density, severe vehicle crashes, and mode choice.<\/p>\n\n
\nblock level; half were classified as “safe cites” (severe\/fatal crash
\nrates one-third of the state average), and half as “less safe cities”
\n(severe\/fatal crash rates close to the state average). Interestingly,
\nthe results showed that the safe cities were well established prior to
\n1950; the less safe cities were largely developed after that time. Even
\nwithin the safe cities, the changes in street network patterns over
\ntime were related to big differences in performance. In the example of
\nDavis, CA, the pre-1940s sections of town (intersection density 211\/sq
\nmi) had a fatal\/severe crash rate that was half the rate of the
\npost-1970 sections of town (intersection density 111-132\/sq mi). The
\nwalking\/biking\/transit mode share was 59 percent in the pre-1940
\nsections of town; in the post-1980 sections of town the
\nwalking\/biking\/transit mode share was 14 percent.<\/p>\n
\ninvestigated street network configuration \u2013 grid patterns, cul-de-sac
\npatterns, and everything in between. The results were consistent across
\nthe board, with highly connected networks of small blocks exhibiting
\nthe best performance in all categories.<\/p>\n