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Sub-problem 1a - Page 7 of 9 |
ID# C201A07 |
Sub-problem 1a: Maxwell Drive PM
Peak Hour - Existing Conditions
Skipped
Phases: Consideration at Maxwell Drive
At Maxwell Drive, the signal phasing is different from
what’s shown in
Exhibit 2-11. First,
the eastbound left lags rather than leads the WB through (and right).
Second, only movement 4 exists to the right of the middle barrier. The
signal phasing is shown in Exhibit 2-12. When movement 5 is green, permissive EB lefts are allowed. If all of the lefts can turn while movement 5 is
green, the 2&5 combination is skipped and the signal progresses from
1&5 directly to 4. If it’s not skipped, the sequence is 1&5,
2&5, and then 4.
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Exhibit 2-12.
Maxwell Drive Phasing Diagram |
How
should this phenomenon be modeled, especially since the HCM doesn’t ask
for dual-ring phasing, minimum greens, maximum greens, gaps, etc. that are
part of an actuated signal? It asks for information about a
prescribed phase sequence where each phase is a specific combination of
green indications. Thus, when a phase is sometimes skipped, what do you
do?The answer is that,
if you're working from observational data alone, then you
adjust the modeled signal timings so that they reflect an
average cycle given that specific phase(s) will sometimes be
skipped. In this case, phase 2 (see
Exhibit 2-5) averages 10 seconds of green
when it comes up, followed by a 3-second yellow and a 1-second
all-red. Since the phase is skipped every other cycle, the signal timings you use in the HCM for this phase
should be: 5 seconds of green, 1.5 seconds of yellow, and 0.5 seconds of
all-red.
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