Problem 3 Discussion - Page 1 of 1
Problem 3: Shenendehowa Campus
So what have we learned?
We’ve seen that you have to be careful in using the peak hour factor.
It’s good to incorporate a peak hour factor, so that the conditions in
the peak 15 minutes are examined. But unless you know the flows all peak
simultaneously, it’s not good to use peak hour factor values that are
movement specific. You’re better off using the value that pertains to
the intersection as a whole during the peak hour. Even that value can lead
to delay estimates that are higher than any real values obtained
during the actual 15-minute intervals. The reason is that the
overall peak hour factor, applied to all of the flows, still assumes
implicitly that all of the movements peak simultaneously and
proportionally as well. Sometimes, as is the case here, that doesn’t
happen. If you find this is a significant issue, you might want to do
analyses for each 15-minute period individually.
We’ve also seen that
it is important to pay attention to the heavy vehicle percentages. This
may be of particular importance in a situation like this, where the Shenendehowa intersection
serves a lot of school buses. We might not initially realize the
importance of accounting for their presence in the traffic stream, but
changes the delays considerably.
Lastly, we’ve seen
that there are ways to check for impacts from site-generated traffic. We
were relatively formal about that, doing the performance assessment with
and without the site-generated traffic, looking at the resulting changes
in delay, and deciding that the impact was insignificant. Sometimes, for expedience, analysts make
a decision based on the percentage increase in intersecting traffic that
results from the site-generated traffic.
you routinely perform sensitivity analyses on the volumes? Planners often use high, low, and base case predictions of
population and traffic growth to bracket possible future conditions. Do you
ever do operational analyses for such conditions or design for such
conditions and consider the incremental impacts?
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