Level of Service. Section 4.5. Level of Service: The Basics. Measure performance by density. Ratio of operating capacity to speed. Units: passenger cars per mile per lane (pc/mi/ln) Denoted by the letters A-F These letters represent the Level of Service (LOS) of the freeway.
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(Values taken from 2000 Highway Capacity Manual, Exhibit 23-2)
Access spacing 2 miles or greater
We then take those base conditions and make adjustments to match the characteristics of our freeway segment!!
Level of Service is determined by the density of traffic in a particular segment, estimated by the following equation:
D = density in pc/mi/ln
Vp =flow rate in pc/h/ln
S = free flow speed in mi/h
GIVEN: Vehicles are counted on a freeway in 5 minute intervals. The highest vehicle count for any one 5 minute segment was 250 vehicles. The total number of vehicles counted for the hour was 2600.
REQUIRED: Compute the Peak Hour Factor
The peak hour factor for this segment of freeway is 0.87
Note that this value is in the typical range for freeway PHF.
These equivalent values can be found in HCM 2000, Exhibit 23-8 or P&P pg. 154
Using the equivalent passenger-car values for level terrain:
The Heavy Vehicle Factor for this segment is 0.98Heavy Vehicle Factor Example
GIVEN: From the previous PHF example, 2600 vehicles are counted on a level freeway segment, of which 90 were trucks & buses and 5 were recreational vehicles.
REQUIRED: Find the heavy vehicle factor for the hour.
Hint: Pay attention to the type of terrain.
Using N = 3 and fDP = 1.00Flow Rate Example
Now that we have all the parts, let’s calculate the flow rate of the freeway segment from our previous examples.
GIVEN: 6 lane freeway in an urban area, level terrain, 2600 vehicles counted in a given hour, and a commuter population.
Recall from previous examples that PHF = 0.87 and fHV = 0.98
REQUIRED: Compute the Flow Rate VP for the segment.
The bottom of the LOS equation is the free flow speed (FFS) of the highway segment. Free flow speed is measured in miles per hour. The equation for FFS is:
Continuing our previous example, let’s now calculate the free flow speed for the freeway segment.
GIVEN: Added information to previous example, the width of the lanes is 11 feet, the right-side clearance is 5 feet, and there are approximately 1.0 interchanges per mile.
Recall: Urban area, number of lanes N=3
Assume: BFFS = 70 mi/hr
REQUIRED: Calculate the base free-flow speed. Use values from the HCM 2000.
Now that we have all the parts, let’s calculate the density of our freeway segment.
GIVEN: Urban freeway segment.
Vp = 1016 pc/h/ln and S = 62.2 mi/h
REQUIRED: Compute the density and estimate the level of service.
What does it all mean? Click the picture below to get a real life view of Level of Service A:
Now click below to see a shot of LOS C in action: