Chap 4 Cross Section Elements p' 305367

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Chap 4 Cross Section Elements(p. 305367)

• The following topics (pages) are covered in this
  lecture
• Pavement (pp.305-311)
• Lane width (pp.311-312)
• Shoulders (pp. 313-318)
• Drainage Channels (pp.323-329)
• Pedestrian Facilities (pp.357-367)

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Roadway vs. Traveled Way
Roadway The portion of a highway, including
shoulders, for vehicular use. A divided highway
has two or more roadways. Traveled Way The
portion of the roadway for the movement of
vehicles, exclusive of shoulders.
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Typical Cross Section, Normal Crown
High-type surface 1.5 to 2.0 Low-type surface
2 to 6
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Typical Cross Section, Superelevated
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Roadway Sections for Divided Highway
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Lane Width

• 9 to12 ft, 12 ft predominant
• 11 ft acceptable
• 9 ft acceptable for low-volume roads in rural
  suburban areas
• Narrow inside lanes may be OK, like 10 to 11 ft
  inside lanes and 12 to 13 ft outside lanes to
  accommodate bikes
• Auxiliary lanes (like left turn lanes) can be 10
  ft, but TWLTL should have 10- to 16-ft

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Shoulders
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Importance of Shoulders

• Space for vehicles with problems to park
• Space for drivers to stop and check maps, etc
• Space for evasive maneuvers to avoid collisions
• The sense of openness
• Help providing required sight distance
• Increased aesthetics
• Improved capacity
• Space for maintenance operations (snow storage)
• Lateral clearance for signs and guardrails
• Discharge storm water away from the edge of
  pavement (reduce pavement breakup)
• Structural support for the pavement
• Space for pedestrians and bicycles

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Shoulder Width

• Desirably, a vehicle stopped on the shoulder
  should clear the edge of the traveled way by at
  least 1 ft, and preferably 2 ft. ? 10 ft min
  width
• A minimum of 2 ft for the lowest-type highway,
  and 6 to 8 ft preferred
• A minimum of 10 ft, preferably 12 ft for
  high-type high-volume roads
• A min clearance of 4 ft to barriers
• A shoulder should be continuous

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Shoulder Cross Section

• Depends on the type of shoulder construction
• Bitumen/concrete-surfaced 2 to 6
• Gravel/crushed-rock 4 to 6
• Turf 6 to 8
• The max algebraic difference in the traveled way
  and shoulder grades should be from 6 to 7 (be
  careful especially at the higher side of the
  segments with superelevation (i.e., grade break)

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Shoulder Stability

• Paved or stabilized shoulders offer numerous
  advantages
• Provision of refuge for vehicles during emergency
• Elimination of rutting and drop-off adjacent to
  the edge of the traveled way
• Provision of adequate cross slope for drainage of
  roadway
• Reduction of maintenance, and
• Provision of lateral support for roadway base and
  surface course

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Drainage Channels and Sideslopes

• Drainage channels should have adequate capacity
  for the design runoff, provide for unusual storm
  water with minimum damage to the highway, and be
  located and shaped to provide a safe transition
  from the roadway to the back slope.
• Drainage channels include (1) roadside channels
  in cut sections, (2) toe-of-slope channels to
  convey the water from any cut section to the
  natural watercourse, (3) intercepting channels
  placed back of the top of cut slopes to intercept
  surface water, and (4) flumes to carry collected
  water down steep cut or fill slopes.

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Sideslopes
Foreslope 1V4H or flatter recommended Backslope
1V3H or flatter recommended (if steeper than
1V2H, consider retaining walls
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Pedestrian Facilities, p.357
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Sidewalks

• 8 ft considered an appropriate minimum
• In residential areas, 4 to 8 ft
• A planted strip between the traveled way and
  sidewalk, min 2 ft
• Where sidewalks placed adjacent to the curb, make
  it 2 ft wider
• In general, wherever roadside and land
  development conditions affect regular pedestrian
  movement along a highway, a sidewalk or path
  area, as suitable to the conditions, should be
  furnished.
• AS a general practice, sidewalks should be
  constructed along any street or highway not
  provided with shoulders, even through pedestrian
  traffic may be light.
• Sidewalks should have all-weather surface to
  endure their intended use.

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Design a cross section and cutting cross sections

• We will use the sample design case given to you
  beginning Homework 6.
• First design a cross section template.
• Cut cross sections along the best route you
  selected
• Can the cut or fill height be contained within
  the maximum value you are given?
• Do you need a berm?