Lecture 5 - Highway Engineering by Dr.Abdul Sami

8/3/2019 Lecture 5 - Highway Engineering by Dr.Abdul Sami

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Design Vehicle


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Design Vehicle

A design vehicle represents an individual class in aconservative manner.

passenger cars (compact, subcompact, light delivery

trucks), trucks (single-unit, tractor-semitrailer combinations,

trucks with full trailers),

buses/recreational vehicles (single-unit, articulated,

school buses, motor homes, passenger cars pullingtrailers or boats).


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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 allaspects 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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Minimum Turning PathPassenger Car

Minimum turning path is

defined by the outer traceof the front overhang and

the path of the inner rear

wheel.


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Minimum

Turning PathDouble-Trailer

Combination


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CUT-AND-COVER


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TUNNEL RAMP UNDER CONSTRUCTION


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Dimensions of Design Vehicle Types


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Operating Characteristics

Acceleration

Deceleration and braking

Power/weight ratios

Headlights

Friction (ball bank)


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Environmental Characteristics

Noise (noise meter)

Exhaust Fuel Efficiency

Dust (particulate and VOCs from tires and

brakes)


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Vehicle Performance

Characteristics

acceleration

decelerationdifficulties in maintaining steady speed

Use

intersections

freeway ramps

climbing or passing lanes, and

turnouts for buses


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Vehicle Performance

Exhibit 2-24


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Vehicle Performance

Exhibit 2-25


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Vehicles on Grades Passenger cars

The upgrades up to 3% have a slight impact onpassenger cars.

On steeper grades this effect becomes more pronounced.

No special consideration is needed.

Trucks

The effect of grades on truckspeeds can be quite strong (Exh. 3-53, 3-60).

The truck with the mass/power ratio 120 kg/kW is selected torepresent heavy vehicles (conservative assumption).

Recreational vehicles

Consideration ofrecreational vehicles on grades can be justifiedfor recreational roads with the low percent of trucks (for example,to consider an additional lane).


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Effect of grade on truck performance

Crawling

speed


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Effect of differential speed on crash

rate


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Critical Lengths ofGrades


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Effect of grade on RV performance


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Maximum Side Friction

Exhibit 3-11


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Friction

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Lecture 5 - Highway Engineering by Dr.Abdul Sami