Sub-problem 2c: Analysis of the South Section of Krome Avenue (Class I Signalized Arterial Facility)

The facility defined by the south section of Krome Avenue was determined in Problem 1 to be a Class I signalized arterial. We must therefore switch chapters from the previous two sub-problems to analyze this facility as an arterial. The planning level procedures for signalized arterial facilities are presented in Chapter 10 of the HCM. Let's review each of these questions and how they are important to this analysis.

What information is gained by performing a planning analysis? Specifically, HCM Exhibit 10-7 gives the estimated service volumes as a function of arterial class and number of lanes in each direction. Because of the assumptions and approximations that support this exhibit, the HCM suggests that the results should not be used for operational analysis or final design.

What assumptions are made when performing an operations analysis on a signalized intersection? Exhibit 3-15 summarizes the assumptions and LOS parameters used in this analysis. The LOS thresholds are taken from the portion of the table that applies to Class I arterials with one lane in each direction. Note that the absence of a threshold entry for LOS A and B indicates that it is not possible to attain either LOS A or B with a free flow speed of 55 mph. Be sure to pay special attention to the turns-from-exclusive-lanes parameter, because this is something that is frequently overlooked or misunderstood.

What is the effect of cycle length on our analysis? For the purpose of our analysis, we have assumed a consistent cycle length of 110 seconds. The HCM suggests that the cycle length may be increased to provide additional capacity at the intersections. Local signal timing policies should be considered to determine whether an increased cycle length is practical. Another approach to consider is to increase the effective g/c ratio for the arterial through movement during the peak periods, allowing over-capacity conditions on the less critical intersecting streets. Queue storage concerns must be carefully weighed in these instances.