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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 whatís 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 itís not skipped, the sequence is 1&5, 2&5, and then 4.

Exhibit 2-12. Maxwell Drive Phasing Diagram

How should this phenomenon be modeled, especially since the HCM doesnít 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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