Getting Started

What Analyses to Perform
The next issue we mentioned was what analyses to perform. In this case study, you need to examine each intersection in each time period, but you also might want to do some specialized analyses, say for heavier-than-typical traffic conditions that arise during special times during the year. You might also want to do a system-level analysis to ensure that you have accounted for all the impacts that arise. We’ll try to answer these questions as the case study proceeds.

For the entire TIA, at least 45 intersection-level analyses are involved. That’s based on five intersections (A, B, C, D, and G), three time periods (AM peak, PM peak, and Saturday midday), and three conditions (existing, future without, and future with). In addition, for the freeway interchange, you need to study at least seven locations: the terminus of the southbound-to-westbound off-ramp, the entrance to the southbound on-ramp, the terminus of the northbound off-ramp (signalized intersection F), the two ramp junctions on I-87 northbound, the ramp junction on I-87 southbound, and the eastbound weaving movement under the I-87 bridges between the southbound-to-eastbound off-ramp and the eastbound-to-northbound on-ramp. That means 63 more analyses: seven locations for three time periods and three conditions.

As indicated, we’re not going to present all 108 analyses. Instead, we’re going to focus on specific problems that let us illustrate how to use the HCM. The problems we are going to consider are listed in Exhibit 2-3.

For each, we’ve identified the situation that will be analyzed (e.g., the school complex entrance during the AM peak) and the learning objectives and analysis issues that will be highlighted by that problem. The issues can be divided into scope (e.g., geographic boundaries, time periods), demands (e.g., demand vs. volume), geometrics, and signal control (e.g., critical movements). After we've completed the problems, we will extend what we’ve observed to speak more generally about conclusions and insights that would relate to the overall TIA. These insights are important to effectively communicate important findings to your audience and the other stakeholders. They also help with sensitivity analysis and ensure that the solutions are feasible.

Discussion:

Take a careful look at the network diagram. What other analyses would you suggest? What ones would you want to include? What overall network do you think should be analyzed if you were doing a traffic impact assessment? Why?