Getting Started - Page 5 of 7
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
communicate important findings to your audience and the other
stakeholders. They also help with sensitivity analysis and ensure that
the solutions are feasible.
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?
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