Roadside Design

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Roadside Design

• FEG 437

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Alleviate the Crash Problem

• 30 of fatal crashes invovle one vehicle
• Opportunity to design forgiving roadsides
• structures

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Clear Recovery Area

• Initial efforts to provide 30 ft of clear
  roadside
• Traversable
• Unobstructed
• AASHTO recommendations based on geometry, volume
  and speed
• Ranges are approximate not absolute
• Economy of project
• History
• Environmental impacts

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Clear Zone Distances
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Horizontal Curve Adjustment
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Horizontal Curve Adjustment

• Example
• V 60 mph
• ADT 2300 vpd
• Foreslope 1V8H
• Tree located 32 ft from outside travel lane
• R1300 ft
• 1st find clearance for straight section
• is CZ OK?

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Horizontal Curve Adjustment

• 32 ft gt 30 ft OK
• V 60 mph
• ADT 2300 vpd
• Foreslope 1V8H
• Tree located 32 ft from outside travel lane
• R1300 ft
• Apply curve adjustment find K
• CZ (lower) 26 x 1.4 36
• CZ (upper) 20 x 1.4 42
• 32 lt 36 and 42, so not OK
• What if tree is 32 from inside lane?

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Topogaraphy

• Embankment parallel to traffic flow
• Be aware of critical slope may need barriers to
  restrict access - overturning

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Ditches

• Generally, make ditches as flat as possible
• Consider local conditions
• See chart for V-shape and trapezoidal-shape with
  bottom width lt 4

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Ditches Gradual Slope Change
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