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Human Factors Guidelines for Road Systems - Collection C: Chapters 16, 17, 18, 19, 20, 22 (Tutorials 4, 5, 6), 23 (Updated), 24, 25, 26 (Updated) (2010) / Chapter Skim
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Effects of Posted Speed Limits on Speed Decisions
Pages 17-18

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From page 17...
... For most urban and rural highways, increasing or decreasing the posted speed limits changes 85th percentile speed by approximately 1 to 2 mi/h in the same direction as the change. For interstate freeways, increasing the posted speed limits increases 85th percentile speed by approximately 1 to 3 mi/h.
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From page 18...
... also found that increasing or reducing the posted speed on urban and rural non-limited access roadways did not significantly change the number of injury or fatal crashes. Overall, changes in speed limits seem to simply legalize existing driver behavior; that is, they change compliance levels rather than speeding behavior.
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Key Terms

  • posted speed
  • speed limit
  • appropriate speed
  • exceeded posted
  • speed dispersion

  • speed choice
  • driver speed
  • percentile speed
  • interstate freeways
  • limit changes

  • enforcing speed
  • mph speed
  • speed typically
  • speed compliance
  • maximum speed

  • speed distributions
  • changing speed
  • speed fatalities
  • speed enforcement
  • setting speed

  • speed relative
  • speed changes
  • speed regardless
  • speed appears
  • traffic speed

  • lowering speed
  • increase speed
  • despite larger
  • broad review
  • perceive speeding


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