Debunking Transportation Rules of Thumb

Traffic_night_rules_of_thumb_webWhat a marvelous device are our thumbs. They are so useful that we employ them in a figure of speech: Rules of thumb. Rules of overwhelming consensus, indisputable, golden.

Except when they’re not.

SmartTowns.org shared a blog from economist Joe Cortright dispelling some of the rules of thumb that are gospel to highway engineers and anathema to planners creating places.

Old Rules

  • We should have a high “level of service” on our streets
  • Wider streets are safer streets
  • We should require “enough” off-street parking for every use
  • We should plan for a certain number of car trips to be generated by every land use, no matter where it is.
  • We should have a hierarchy of streets

New rules

  • Slower is safer
  • Sharing is efficient
  • Our objective should be accessibility, not mobility

Cortright’s details for each rule make a compelling case.

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