Design Vehicle

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Design Vehicle

• CE 453 Lecture 6

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Design Vehicle

• Design Vehicle largest (slowest, loudest?)
  vehicle likely to use a facility with
  considerable frequency
• Three characteristics that affect almost all
  aspects of highway design
• Physical
• Operating
• Environmental

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Physical Characteristics

• Type (GB defines 20 design vehicle types)
• Passenger Car P
• Buses B
• Trucks SU, WB
• RVs
• Farm tractor
• Size
• Length
• Height
• Weight
• Width
• Height of drivers eye (car 3.5 avg., truck
  7.6 high side)
• Center of mass

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Dimensions of Design Vehicles
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Operating Characteristics

• Acceleration
• Deceleration and braking
• Power/weight ratios
• Turning radius
• Offtracking
• Headlights (2 truck driver/retroreflectivity?)
• Friction (ball bank)

http//www.cable-car-guy.com/images/ih_truck_ad_de
c_1926.jpg
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Environmental Characteristics

• Noise (noise meter)
• Exhaust
• Fuel Efficiency
• Dust (particulate and VOCs from tires and brakes)

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Selection of Design Vehicle

• Key Controls
• Physical and Operating
• Key Factors
• Proportion and Frequency
• Key Types
• Car parking lot
• SU Truck res. intersections, park roads
• City Bus state hwy, city street, bus route
• See http//www.pacebus.com/sub/guidelines/developm
  ent_guidelines/table20of20contents.htm for
  Chicagos PACE design guide
• School Bus low volume county, state hwy
• WB series freeway ramp, arterial and state hwy,
  industrial areas, US and Interstate highways

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State and Local Truck Limits

• See Colorado Truck Legal Dimensions
• See http//www.dot.state.ia.us/mvd/omve/truckguide
  .pdf for Iowa Truck Guide
• See http//www.co.jasper.ia.us/new_page_7.htm for
  Jasper County permit requirements

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Turn Paths

• Key variables in turn paths
• Centerline turn radius
• Out-to-out track
• Wheelbase
• Path of inner tire
• See Autoturn Software Page http//www.transoftsolu
  tions.com/transoft/products/at/product_feat.asp

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Minimum Turning Radii
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Offtracking

• Rear wheels do not follow path of front wheels
  (see slide 29)
• Increases with size of vehicle
• Decreases with radius of curve
• Track width can be calculated using

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Rear Steering
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Front Overhang and Difficulty Adjustment (Z)

• Radial distance between outside front wheel path
  and outside front bumper/fender
• Extra width allowance (Z) for difficulty in
  maneuvering

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Total widening recommended (includes front
overhang, offtracking and difficulty adj.)
Double for 4 ln undivided. Values less than 2
may be neglected.
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Widening

• Widen inside only when not using spiral (split
  even if using spirals)
• Paint CL and joint at middle of pavement
• Transition over superelevation transition
• Green book terminology

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Effect of grade on truck performance
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Effect of grade on RV performance
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Effect of differential speed on crash rate
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Critical Grade

• AND length of grade where typical trucks can
  maintain a safe speed

See also Highway Capacity Manual
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Friction
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What is a turning template?

• For the various design vehicles, the turning
  templates give the minimum vehicle paths
• Based on low speed (10mph)

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What do I use it for?

• Use in design, to determine vehicle fit
• Curbs etc 2-3 feet outside of the minimum path
  limits
• With 2 different vehicles larger minimum radius
  governs

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Homework Assignment

• Due Wednesday
• Review and compare the templates for the SU
  (single unit truck) and the Bus-40 (40-ft bus)

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Homework Assignment

• Answer the following questions regarding these
  two design vehicles and their templates
• What is the difference in
• minimum outside turning radii?
• centerline turning radii?
• maximum off-tracking?
• minimum path of right rear wheel?

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Homework Assignment

• Provide a bullet point summary of your answers to
  these questions.
• Then discuss whether or not the use of one or the
  other as the design vehicle for an intersection
  would have an impact on your design of an
  intersection and its corner radius, and why.
  Cite the results of your comparison (of the
  template) to support your position.
• Maximum one page.