Subproblem 1b  Page 7 of 7 
ID# C401B07 
Subproblem 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 15minute flow rate (v_{p}),
passenger car speed, and density. Subordinate tables contain the lane width,
the righthand 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 15minute data), and S the passenger car
speed for the peak 15minute time period. P_{T} is set to 5%,
P_{R} is set to 0%, and f_{p} is set to 1.0
Exhibit 413. Peak Hour LOS Distribution 
LOS 
Max D 
# Hours 
Percent 
A 
11 
7 
2.7% 
B 
18 
7 
2.7% 
C 
26 
17 
6.6% 
D 
35 
208 
81.3% 
E 
45 
13 
5.1% 
F 
 
4 
1.6% 
Our findings are shown
in Exhibit 413 and Exhibit 414. 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 413 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 heavilytraveled 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.
