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Design Vehicle

Learn how physical, operating, and environmental characteristics of design vehicles influence highway design considerations. Discover key controls, factors, and selection criteria for different vehicle types. Explore turning paths, offtracking, and widening recommendations.

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Design Vehicle

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  1. Design Vehicle CE 453 Lecture 6

  2. 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

  3. 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 driver’s eye (car: 3.5’ – avg., truck: 7.6’ – high side) • Center of mass

  4. Dimensions of Design Vehicles

  5. 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_dec_1926.jpg

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

  7. 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/development_guidelines/table%20of%20contents.htm for Chicago’s PACE design guide • School Bus – low vol county, state hwy • WB series – freeway ramp, arterial and state hwy, industrial areas, US and Interstate Highways

  8. 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

  9. 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.transoftsolutions.com/transoft/products/at/product_feat.asp

  10. Minimum Turning Radii

  11. Offtracking • Rear wheels do not follow path of front wheels • Increases with size of vehicle • Decreases with radius of curve

  12. 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

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

  14. 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:

  15. Effect of grade on truck performance

  16. Effect of grade on RV performance

  17. Effect of differential speed on crash rate

  18. Critical Grade • % AND length of grade where “typical” trucks can maintain a “safe” speed See also: Highway Capacity Manual

  19. Friction

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