Sub-problem 2b: What are the Levels of Service in the Weaving Sections Located in the I-87/Alternate Route 7 Interchange?

By referring once again to the summary of results presented in Exhibit 4-28 we see much higher flow rates in the PM peak than in the AM peak, 5,447 veh/hr in the PM and only 2,196 veh/hr in the AM. And, while there is a very high volume ratio (VR) during both periods, the lower total volumes mitigate this condition in the AM peak. However, in the PM peak, the high volume ratio combined with the high overall flow rates result in an overall speed of 31.7 mi/hr in the weaving section and a density of 38.2 pc/mi/lane.

Furthermore, both the volume ratio and the total weaving volume model limits are exceeded during the PM peak. The likely result is a breakdown of operations and queuing at some locations in the section. We should note that the volume ratio limit is also exceeded in the AM peak, again resulting in poor operations.

We can conclude that, even though the forecasted level of service is B for the AM peak, both time periods will experience poor operations with breakdowns in flow to be expected. While we won't consider this sub-problem in more detail here, it would be valuable for you to review the results presented here and identify geometric improvements that you think might improve the operational performance of this weaving section.

The operation of Weave C is even worse, with forecasts of level of service F for the AM peak and level of service E for the PM peak. With the high density and the failing conditions present for this analysis, we might ask whether or not we should consider another tool in addition to the HCM, such as a microscopic simulation model, to evaluate this weaving section. We will discuss this issue in more detail in Problem 5 of Case Study 4.