Describe the factors that affect the level of service of a freeway section and the impact each has on flow.

Question

What will be an ideal response?

Answer 1

Lane width – Traffic is restricted when lane widths are narrower than 12 ft.
Motorists tend to travel more cautiously because of the reduced lateral distance
between vehicles by reducing their speeds.
Lateral clearance – Lateral obstructions tend to have an effect similar to reduced
lane width. Drivers in the lane adjacent to the obstruction will tend to shy away
from the obstruction, moving them closer to vehicles in the adjacent lane and
resulting in a reduction in speeds. Lateral obstructions more than 6 ft from the
edge of the traveled lane have no significant effect of traffic flow.
Traffic composition – The effect of large or heavy vehicles in the traffic stream
reduces the maximum flow on the highway because of operating characteristics; a
heavy vehicle occupies more space in the traffic stream than does a passenger car.
Grade – The effect of a grade depends on the length and slope of the grade.
Traffic operations are significantly affected when grades of 3% or greater are 0.25
mile or greater in length and when grades of 3% or less are greater than 0.5 mile
in length. The effect of grades on heavy vehicles is much greater than on
passenger cars.
Driver population – A driver population consisting primarily of weekday
commuters will have significantly different behavior than a driver population
consisting of drivers unfamiliar with the roadway. For example, recreational
traffic capacities can be as much as 20% lower than commuter traffic capacities.
Interchange spacing – As interchanges are more closely spaced, the lengths of
basic freeway segments unaffected by interchanges decreases as the weaving
movements at interchanges have an increasing impact on traffic flow resulting in
a reduction of speeds.