Problem 4: Discussion

The freeway facility methodology from chapter 22 of the HCM has provided us with important insights on the performance of Alternate Route 7 during both the off peak and peak periods. We found the facility performs well during the off peak, but the lane drop from three to two lanes on the eastbound portion of the facility results in some delay for motorists during the PM peak period.

We also need to consider whether further analyses should be conducted to have a complete picture of the operation of this facility. Let's consider the following issues:

The system that we considered is the mainline portion of Alternate Route 7 from the I-87 interchange on the west to the I-787 interchange on the east. But do we need to extend the boundary of our study area further in order to capture any other effects? We know that there are problems with the interchanges themselves. Some of these problems appeared in the analysis that we conducted for problems 2 and 3 of this case study. So, widening the system to include the interchanges might prove beneficial in our assessment of Alternate Route 7.

This leads to the next issue, the possible use of micro-simulation. Under what conditions should we consider micro-simulation modeling? The first such condition is when demand exceeds capacity, particularly when there is an intersection of queues on the facility. Here, there is value in the ability of a micro-simulation model to follow the behavior of individual vehicles and drivers as they negotiate a congested facility. A second such condition is when we are considering a large and complex system, such as a freeway mainline and interchanges.

In problem 5 of this case study, we will illustrate how one micro-simulation tool can be used to study the operation of Alternate Route 7.