Problem 2: Operational analysis of the I-87/Alternate Route 7 Interchange

Looking again at Exhibit 4-18, you can see that all southbound vehicles wanting either Exit 6 or Exit 7 have to leave I-87 at the top of the diagram. Those going to Alternate Route 7 east diverge where the loop ramp turns west. Those going to Exit 6 continue south. Vehicles coming south from I-87 toward Exit 6 weave through the vehicles from the semi-direct ramp to I-87 south. A high percentage of vehicles on the semi-direct ramp have to cross the I-87 traffic going to Exit 6 then use the single lane slip ramp south of Location C to get to I-87. This difficult weave is one of the places analyzed in this problem.

Now that you know some important details on the geometry of the interchange, let's consider the problem at hand, the completion of an operational analysis of the interchange. We will consider two specific procedures from the HCM, one to analyze weaving sections and the other to analyze ramp junctions. We will illustrate these two procedures using the four sub-problems listed below.

Sub-problem 2a. What types of analysis should be conducted on the I-87/Alternate Route 7 interchange?
Sub-problem 2b. What are the levels of service in the weaving sections located in the I-87/Alternate Route 7 interchange? These sections are noted as points A, B, and C in the interchange sketch.
Sub-problem 2c.What are the levels of service along the ramp and at the ramp junction for the on-ramp from Alternate Route 7 to I-87 northbound? This section is noted as point D in the intersection sketch.
Sub-problem 2d. What is the effect of making geometric improvements to the ramp and at the ramp junction for the on-ramp from Alternate Route 7 to I-87 northbound?