CE 453 Lecture 6 Design Vehicle Design Vehicle

CE 453 Lecture 6 Design Vehicle

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 2

Physical Characteristics ► Type (GB defines 20 design vehicle types) § § § ► Passenger Car P Buses B Trucks SU, WB RVs Farm tractor Size § § § Length Height Width Height of driver’s eye (car: 3. 5’ – avg. , truck: 7. 6’ – high side) Center of mass 3

Dimensions of Design Vehicles 4

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 5

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

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/ta ble%20 of%20 contents. 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 7

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 8

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/p roducts/at/product_feat. asp 9

Minimum Turning Radii 10

11

Offtracking ► Rear wheels do not follow path of front wheels ► Increases with size of vehicle ► Decreases with radius of curve 12

13

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 14

15

16

Total widening recommended (includes front overhang, offtracking and difficulty adj. ) Double for 4 ln undivided. Values less than 2’ may be neglected. 17

18

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: 19

Effect of grade on truck performance 20

Effect of grade on RV performance 21

Effect of differential speed on crash rate 22

Critical Grade ►% AND length of grade where “typical” trucks can maintain a “safe” speed See also: Highway Capacity Manual 23

Friction 24

25

26

27