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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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Speeding Countermeasures: Setting Appropriate Speed Limits
Pages 19-20

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From page 19...
... Objective General Strategy Design Guideline Consider the: Design speed of a major portion of the road, Vehicle operating speed, measured as a range of Set speed limits that account 85th percentile speeds taken from spot speed for roadway design, as well surveys of free-flowing vehicles on the roadway, as traffic and environmental Safety experience of the roadway, in the form of conditions crash frequencies and outcomes, and Enforcement experience; i.e., law enforcement's allowance for driving above the posted speed limit as well as the level of enforcement. Set appropriate While the efficacy of VSLs is uncertain (see also speed limits Milliken et al.
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From page 20...
... The use of differential speed limits for heavy trucks is an option for locations associated with a high incidence of truck crashes; however, the research is mixed with respect to the efficacy of doing so. The logic underlying the use of having a lower posted speed limit for trucks than for passenger vehicles is "that trucks have much longer stopping distances than do light vehicles and have other speed-related risks such as rollover at lower speeds and vulnerability to loss of control in cross winds" (3)
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Key Terms

  • appropriate speed
  • traffic control
  • roadway design
  • differential speed
  • speed limit

  • highway safety
  • safety plan
  • control elements
  • using roadway
  • strategic highway

  • communicating appropriate
  • aashto strategic
  • posted speed
  • set speed
  • variable speed

  • companion guidelines
  • research board
  • heavy trucks
  • transportation research
  • expert judgment

  • collisions involving
  • predictable events
  • actual driving
  • school hours
  • enforcing speed

  • enforcement officers
  • driver expectancies
  • key considerations
  • legal limit
  • involving heavy


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