Sub-problem 1b: Maxwell Drive PM Peak Hour - With Conditions

Operational versus Planning Analyses
In all the analyses we’ve done so far for the PM With condition, we’ve done planning level analyses using the HCM and we’ve explored the use of critical lane analysis. We can also evaluate signal timings and lane configurations, at a more detailed level, using an operational level analysis.

We don’t need to explore all of the configuration options presented in Exhibit 2-15 and Exhibit 2-16. Only a few of them are worth investigating further. From Exhibit 2-16, let’s look at scenarios C-4, C-7, and C-8. 

In the case of Scenario C-4, we have single left-turn lanes eastbound and westbound as well as two through lanes, shared with the rights. Northbound and southbound, we have single left-turn lanes and separate lanes for the throughs and rights. The detail that distinguishes it from Scenario C-1 is that the northbound and southbound rights can move concurrent with the eastbound and westbound lefts. That allows the cycle length to be much shorter. Dataset 10 (C-4), Dataset 11 (C-7) and Dataset 12 (C-8) contain the input data these three scenarios.

As Exhibit 2-17 shows for Scenario C-4, a cycle length of 65 seconds can be obtained using the operational analysis.  This cycle length is much shorter then the 114.9 second cycle length that was obtained from the critical movement analysis. The overall delay is 28.7 seconds, the maximum delay is 39.5 (northbound through), and the maximum average queue is 17.6 vehicles (westbound through-and-right). For Scenario C-7, a 90-second cycle length from the operational analysis is compared to a 106.7 second cycle length from the planning analysis. The delays and queue lengths are considerably larger than C-4, so the C-7 solution is not better. For C-8, we can’t match the 84.4 seconds from the critical lane analysis. The shortest cycle length we can make work is 93.0 Some movements have LOS F if the cycle length is shorter.

What have we learned from this? We’ve seen that we can make the signal work, in an operational analysis, for the conditions that the planning analyses suggested should work. We have also seen that the cycle lengths are sometimes different. One final observation is that it seems possible with the operational analysis to fine-tune the problem solution in some cases so that better than at-capacity performance can be achieved through careful selection of the phasing plan and the lane configuration.