Highway Engineering
When the speed of traffic flow becomes zero,then

traffic density and traffic volume both become zero
traffic density and traffic volume both attain maximum value
traffic density attains maximum value whereas traffic volume becomes zero
traffic density becomes zero whereas traffic volume attains maximum value

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Highway Engineering
Length of a vehicle affects

extra width of pavement and minimum turning radius
clearance to be provided under structures such as overbridges, under-bridges etc.
width of traffic lanes
width of shoulders and parking facilities

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