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Subproblem 2a - Page 3 of 3

ID# C302A03

Sub-problem 2a: Analysis of the North Section of Krome Avenue (Class I Two-lane highway Facility)

Exhibit 3-13. North Section Planning Level Estimation Based on HCM Exhibit 12-15 Assumptions

Terrain Level
Posted Speed N/A
Free Flow Speed 55
Directional Split 60/40
Percent Trucks 14
Percent RV's 4
Percent No Passing 20
Design Hour Volume 1,110
Table Thresholds:
LOS A ---
LOS B 330
LOS C 870
LOS D 1,460
LOS E 2,770

Step 2. Results

Exhibit 3-13 shows the results of this analysis. The LOS thresholds are taken from the portion of the table that applies to level terrain with a free-flow speed of 55 mph. Note that the absence of a threshold entry for LOS A indicates that it is not possible to attain LOS A with a free flow speed of 55 mph.

The estimated LOS for this section is D, because the design-hour volume (1,110 vph) exceeds the LOS C threshold (870 vph) but falls below the LOS D threshold (1,460 vph).

HCM Exhibit 12-15 may also be used to project the year in which a given LOS would be exceeded. To illustrate this process, letís determine how many years in the future we would expect the operation to pass from LOS D to LOS E. In other words, we must determine when the volume will increase from 1,110 to 1,460 vph.

The annual growth rate for this highway has been determined to be in the range of 2.4%. At this rate, applying the compound interest formula, we can determine that the volumes will cross the LOS D threshold approximately 12 years in the future.

How useful is a LOS projection based on service volume tables? The projections are based on solid mathematics, but they are also predicated on the assumption that none of the operating parameters (directional split, heavy vehicle percentage, etc.) will change in the future. Therefore, the validity of the projections will be somewhat sensitive to factors such as future roadside development that could shift the table thresholds by lowering the free flow speed. The accuracy of projections of this type is limited by the operating parameters which, in this case, are likely to change over the next ten years. In other words, the operating parameters have a significant impact on the assumptions that are used to create the service volume tables.

Based on our calculations, our estimated level of service is D.

In this sub-problem we have produced an estimate of the LOS for the facility defined by the north section of Krome Avenue, assuming that it operates with the characteristics of typical two-lane highways of the same class. In sub-problem 3a, we will examine the assumptions and substitute observed values to apply the more detailed operational procedures described in Chapter 20 of the HCM.

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