Sub-problem 1b: Analysis of the Eastbound Freeway Section

The question we’re trying to answer is this: What is the performance of this facility like during a reasonably heavy AM peak hour (some might refer to this as the design hour)? To answer the question, we constructed a spreadsheet that implements the HCM methodology shown in Equations (1)-(4) in a single row of a spreadsheet. The spreadsheet contains a column for each of the following data items: day of the year, day of the week, hour, eastbound volume, eastbound PHF, percent trucks, percent recreational vehicles, heavy vehicle factor, driver population factor, peak 15-minute flow rate (v_p), passenger car speed, and density. Subordinate tables contain the lane width, the right-hand shoulder clearance, and the number of lanes.

Three of these data items are derived from the monitoring station data: V, the volume for the hour; PHF, the peak hour factor (since these can be computed from the underlying 15-minute data), and S the passenger car speed for the peak 15-minute time period. P_T is set to 5%, P_R is set to 0%, and f_p is set to 1.0

Our findings are shown in Exhibit 4-13 and Exhibit 4-14. For 208 of the 256 AM peak hours, or about 81.3%, the LOS is D. That’s significant news. The predominant LOS is clearly D. For 5.1% of the peak hours it is E, for 1.6% it is F and for 6.6% it is C. (The remaining 5.4% of the time it is A or B, probably on weekdays that are holidays.) This seems consistent with field observations.

The implications of Exhibit 4-13 are clear in terms of characterizing the performance of the facility. You can be comfortable describing its average condition as D. You could say that most of the time the LOS is D, in some heavily-traveled hours (6.7% of the time or about once every two weeks) the LOS is E or F, and the rest of the time it is A, B, or C. Chances are, your audience will understand that. Certainly, your fellow traffic engineers will.