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Human Factors Guidelines for Road Systems, Collection B: Chapters 6, 22 (Tutorial 3), and 23 (Updated) (2009) / Chapter Skim
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The Influence of Perceptual Factors on Curve Driving
Pages 4-5

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From page 4...
... Potential encroachment 8000 8000 Recommended Range 7000 Recommended 7000 e Actual Curvature Range ng 6000 e 6000 Ra ng le Ideal trajectory Ra p ta b Trajectory along 5000 le 5000 ce pta b Ac apparent curvature 4000 ce 4000 Ac 3000 3000 2000 2000 Curve entry speed based on 1000 Unacceptable Range 1000 Unacceptable Range apparent curvature is too high to safety traverse the actual curvature 0 0 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 Radius of Horizontal Curve (m) Radius of Horizontal Curve (m)
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From page 5...
... While no specific values or recommendations can be made for these aspects, it is useful to take them into consideration during curve design, especially if other aspects of the curve design suggest that there may be a potential problem with driver perception of the curve radius. Aspect Effect Empirical Support Superimposed Vertical Sag Makes a curve appear flatter Strong Cross Slope For sag horizontal curves, the greater the cross slope and lane width, the Analytical evidence greater the apparent flattening of the horizontal curve Superimposed Vertical Crest Makes a curve appear sharper and may cause discontinuities in curve Strong Deflection Angle Holding radius constant, greater deflection angle makes the curve Moderate appear sharper, especially for smaller radii Delineators Delineators provide drivers with more information to judge the curve Moderate radius, which improves accuracy of these judgments Spiral May make curve appear flatter, or make curve perception more Indirect difficult, because the onset of the curve is less apparent Signage Drivers perceive curve as "riskier" if signs indicate that the curve is Suggestive hazardous Cross References Task Analysis of Curve Driving, 6-2 Key References 1.
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Key Terms

  • curve entry
  • horizontal curves
  • curve driving
  • visual distortion
  • curve appear

  • curve radius
  • curve perception
  • sag horizontal
  • entry speeds
  • vertical sag

  • vertical curvature
  • plan radius
  • appear flatter
  • speed selection
  • appear sharper

  • unacceptable range
  • curve design
  • regarding curve
  • crest horizontal
  • apparent radius

  • superimposed vertical
  • vertical alignment
  • entry speed
  • visual image
  • visual information

  • driver expectations
  • radius appears
  • driver perception
  • radius combinations
  • primary basis


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