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Subproblem 3a - Page 2 of 5

ID# C303A02

Sub-problem 3a: Analysis of the North Section of Krome Avenue (Class I Two-lane Highway Facility)

In sub-problem 2a, we 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 this sub-problem, we will examine the assumptions and substitute observed values for this section to apply the more detailed operational procedures.

What is the difference between the planning and operations level analyses? It is important to recognize the difference between the planning and operational level procedures. The operational procedure estimates the level of service from computed performance measures that are compared against established LOS thresholds for those measures. The two performance measures are percent time spent following (PTSF) and average travel speed (ATS). The LOS thresholds for these measures are shown in Exhibit 3-17 for a Class I two-lane highway. For this highway class, the more critical of the two measures will determine the LOS.

Exhibit 3-17. LOS Thresholds for Class I Two-Lane Highways


Percent Time-Spent-Following

Average Travel Speed (mph)
















The planning level procedure presented in HCM Chapter 12 was derived from the operational procedure, assuming typical values for all operating parameters. The service volume table in HCM Exhibit 12-15 was produced by applying the operational procedure repetitively with different volumes and noting the volume levels at which the LOS changed from one value to the next. As such, the service volume table results should be identical to the operational level results, but only when the same operating parameters are applied to both procedures.

For example, the service volume tables presented in the HCM and used within the planning analysis assumes 14% trucks and buses. Data collected for Krome Avenue indicates the corresponding value for Krome Avenue is 27%. Similarly, the default peak hour factor for rural conditions assumed in the HCM is 0.88, whereas the actual measured PHF is 0.94. The differences between these values will cause the results of the two methods to depart from each other; and the operational level results must be considered more accurate, because they are based on actual field data instead of assumptions that do not apply to the facility under study.

Planning-level analyses are appropriate when operational parameters do not exist (for example, in a future-year analysis) or cannot be feasibly obtained. In such circumstances, detailed analysis such as queue length estimates are not appropriate because the quality of the available data does not support this level of analysis.

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