Sub-problem 2a: What types of analysis should be conducted on the I-87/Alternate Route 7 interchange?

These points can be analyzed using HCM Chapter 25. The other points can also be evaluated to determine the adequacy of their capacity, but the HCM procedures do not apply to the merge operations at these points. Note that the other merge and diverge points on the freeway segments that constitute this interchange are part of weaving sections and are discussed below.

Let's now consider the weaving sections. They are composed of these on- and off-ramps that are no longer than 2,500 feet apart, or slightly less than one-half mile. If the ramps are spaced more than 2,500 feet apart, the turbulence resulting from the lane changing is limited to the vicinity of the ramps themselves, rather than being the combined effect of the on and off-ramps.

There are three weaving sections in this interchange:

1. northbound I-87 between the entrance ramp from State Route 2 and 7 to the exit ramp to eastbound Alternate Route 7

2. southbound I-87 between the frontage road entrance ramp from Alternate Route 7 to the I-87 southbound mainline

3. eastbound Alternate Route 7 between the entrance ramp from I-87 northbound and the exit ramp to U.S. 9

In order to assess the overall operation of the interchange, with its four ramp junctions and three weaving sections, we would need to evaluate the level of service at each one. However, in the interest of time, we will limit our focus here to the three weaving sections and one ramp junction.

When you are ready, proceed to Sub-problem 2b.