Geometric

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Geometric Pavement DesignExample Problems
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Problem 3.15
Due to crashes at a railroad crossing, an
overpass (with a surface 24 ft above the existing
road) is to be constructed on an existing level
highway. The existing highway has a design speed
of 50 mph. The overpass structure is to be
level, centered above the railroad, and 200 ft
long. What length of the existing level highway
must be reconstructed to provide an appropriate
vertical alignment?
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Problem 3.27
A developer is having a single-lane raceway
constructed with a 100 mph design speed. A curve
on the raceway has a radius of 1000 ft, a central
angle of 30 degrees, and PI stationing at
112510. If the design coefficient of side
friction is 0.20, determine the superelevation
required at design speed (do not ignore the
normal component of the centripetal force).
Also, compute the degree of curve, length of
curve, and stationing of the PC and PT.
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Geometric Design Example

• A 2-lane (10 ft wide lanes) combined horizontal
  and crest vertical curve is currently posted for
  a 35 mph speed limit and is designed for 40 mph.
  Curve data are
• Horizontal L 580 ft, ? 60, e 6, Ms 30
  ft
• Vertical L 580 ft, G1 3, G2 -2.5
• Is this curve adequately designed for 40 mph?
• Because this curve is often covered in packed
  snow and ice, the county wants to post a
  recommended speed limit for these conditions.
  What speed limit do you recommend?

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Problem 3.37

• Two straight sections of freeway cross at a right
  angle. At the point of crossing, the east-west
  highway is at elevation 150 ft and is a constant
  5.0 grade (upgrade in the east direction), the
  north-south highway is at elevation 125 ft and is
  a constant -3.0 grade (downgrade in the north
  direction). Design a 90-degree ramp that
  connects the northbound direction of travel to
  the eastbound direction of travel.
• Design the ramp for the highest design speed (to
  the nearest 5 mph) without exceeding a minimum D
  of 8.0. (Assume the PC of the horizontal curve
  is at station 1500, and the vertical curve PVIs
  are at the PC and PT of the horizontal curve).
  Maximum allowed superelevation by design
  standards is 12.
• Determine the following
• Stationing and elevations of the horizontal curve
  PC and PT
• Horizontal curve radius and length
• Stationing and elevations of the vertical curve
  PVCs and PVTs
• Vertical curve lengths
• Length of constant grade in between the 2
  vertical curves (if any)

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North
Downhill (-3.0)
Uphill (5.0)
EW freeway
Elevation difference 25 ft
NS freeway
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Pavement Design Example

• The pavement on Stevens way is slowly being
  switched to PCC a few thousand yards at a time.
  Assuming all the heavy vehicle traffic on Stevens
  Way is due to bus traffic, estimate a rigid
  pavement design using the following data
• Design life 40 years
• Articulated bus average axle weights
• Front 15,000 lb
• Middle 18,500 lb
• Rear 11,500 lb
• Regular (non-articulated) bus average axle
  weights
• Front 12,200 lb
• Rear 20,000 lb
• Typical school day 80 regular, 40 articulated
  in one direction
• Bus traffic growth rate 2 per year
• Use undowel joints and crushed stone base
  material

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Pavement Design Example

• What would a flexible pavement design be for the
  same loading? Assume
• Two layers (HMA and a granular base course)
• Subgrade MR 10,000 psi