Appurtenances

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Appurtenances

• HDM Ch. 10

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Kinetic Energy (g-forces)

• A car weighs 3000 pounds
• At 20 mph KE40,000 ft-lb (0.5mv2)
• At 40 mph KE160,000 ft-lb
• If the car above stops in 50 ft
• Average deceleration in gs is 1.07 for a car
  starting at 40 mph

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Equations

• Kinetic Energy 0.5MassV2
• Avg Deceleration (in gs) for a car at some
  initial speed decelerating to a stopping
  condition over some length L
• V2/(2gL)

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Appurtenances

• When vehicles leave the roadway how can you
  reduce the and severity of accidents?

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Clear Zone

• Area free of hazardous objects and gently
  graded to permit reasonably safe re-entry to the
  highway or provide adequate distance for stopping
• References AASHTO Green Book
• AASHTO Roadside Design Guide

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New Reconstructed

• Provide satisfactory clear zones when practical
  and provide barriers if not
• Clear zone includes
• -Shoulder
• -Recoverable slope (or traversable slope and
  clear runout width)

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Clear Zone

• Based on
• Design Speed
• Traffic Volume
• Roadside Slope
• Curvature of the Road

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Basic Recovery Width (BRW)

• Basic width of recovery area that should be
  provided (see Table 10-1)
• BRW does not consider curvature, non-recoverable
  slopes or accident history

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Non-Recoverable Slope

• Slope at which it is unlikely a driver will be
  able to regain control of a vehicle and return to
  the roadway (vehicle will continue to the bottom
  of the slope)
• Embankment slopes steeper than 14 are considered
  non-recoverable
• Traversable, non-recoverable slopes can be
  present in the clear zone, but do not count
  towards the BRW

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Curve-Corrected Recovery Width (CCRW)

• Takes into account effects of horizontal
  curvature
• Obtain by multiplying BRW by the horizontal curve
  correction factor found in Table 10-2
• Apply factor when long tangents are followed by a
  curve rated 15 km/hr less than the operating
  tangent speed

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Clear Runout Width (CRW)

• Width provided at the toe of a traversable,
  non-recoverable fill slope
• Minimum width should be 2.5 m (why that ?)

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Desired Minimum Clear Zone Width

• Larger of
• BRW
• CCRW
• Sum of CCRW plus the width from the traveled way
  to the toe of the traversable but non-recoverable
  slope

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Design Clear Zone Width

• Should be at least the minimum and preferably
  greater than the minimum

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Point of Need

• Fixed object
• use 15-deg divergence angle
• use 10-deg on freeways/interstates

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Deflection Distance

• Distance that the outside face line of a barrier
  will deflect when struck by a vehicle
• See Table 10-3 (based on 100km/hr 2000 kg
  vehicle, 25 deg angle)
• Deflection distance behind barriers must be kept
  free of FOs

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Barrier Types

• Cable Guide Rail
• Corrugated Metal (W-beam) (1.5cable)
• Box Beam (3cable)
• Concrete (10cable)

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Median Barriers

• Designed to withstand impact from either side
• Corrugated metal beam
• Box Beam
• Concrete

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Selecting Guide Rail

• Choose barrier w/ largest acceptable deflection
• Deflection must be less than distance from
  barrier line to nearest hazard that cant be
  removed or relocated
• Maintain area behind guide railing
• (tree dia. gt 100 mm is considered a hazard)
• Deflections must stay within ROW

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Potential Hazards

• Potential fatalities
• Cliff
• Deep body of water
• Flammable liquids tank
• Fixed Objects
• Bridge piers/abutments
• Trees (gt100mm)
• Utility Poles
• Buildings
• Retaining Walls
• Overhead sign structures

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Potential Hazards (continued)

• Roadside Obstacles
• Rock cuts
• Longitudinal retaining walls
• Ditches
• Cliffs
• Dropoffs
• Bodies of Water
• Projectiles
• Mailboxes
• Fence Rails

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Treatment Options

• Remove from clear zone
• Relocate
• Modify
• Replace concrete headwall w/ flared end
• Pour a smooth concrete wall against a rock cut
• Place grates across drain pipe end sections
• Replace posts w/ break-away posts
• Shield
• Guide railing
• Impact attenuators
• Delineate

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Impact Attenuators

• Used when fixed hazards cant be removed or
  protected by railing (gore areas)
• Inertial Systems-Transfers kinetic energy to
  series of yielding masses (sand barrels)

http//www.crashcushions.com/rental.php
http//epg.modot.org/index.php?titleCategory612_
impact_attenuators
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Impact Attenuators

• Compression Systems-Absorbs energy by progressive
  deformation or crushing of the system elements
  (GREAT-Guardrail Energy Absorbing Terminal)

http//www.acprod.com.au/images/product/ACP-NSW__S
KT_product_brochure_1.jpg
http//www.highwaysafety.net/endTreatments.htm
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Guiderail is a Type 3 Box with a 'WYBET' terminal
section.Picture taken in June 2011Location
Interstate 81 south in the town of Castle Creek,
NY---from SUNYIT student who works for NYSDOT
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Vaulting

• When vehicle vaults over a barrier
• Free to hit a FO
• May roll over
• Major Cause (Curbs)
• Dont use curbs w/ concrete barriers or cable
• Minimize use of mountable curbs
• Dont use non-mountable curbing when operating
  speeds are gt80 km/hr
• Place curbs lt1 or more than 10 from guide
  railing

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Other

• Fencing and cattle passes keep livestock and wild
  animals from entering the traveled way

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Innovative Median Barriers

• Single Slope Concrete Median Barrier
• Moveable Concrete Barrier
• Truck Barrier
• Cable Median Barrier