Sub-problem 1a - Page 3 of 8 |
ID# C101A03 |
Sub-problem 1a: Analysis of the
existing TWSC intersection
Following are other points to consider regarding the
required data:
| Traffic volumes for each movement were obtained
from two sources. The existing traffic volumes (See
Exhibit 1-7) reflect the results of a manual traffic count conducted
during the afternoon peak hour. The future traffic volumes (see
Exhibit 1-8) reflect a horizon year ten years hence and come from the
application of an historical growth trend that has been observed on US 95
over the past ten years. We are assuming, based on our own familiarity
with the area, that there is no significant volume of pedestrian crossings
at the intersection which might impede the flow of vehicles. |
| The number of lanes and lane configuration
for each approach can be determined from the
aerial photograph. |
| Heavy vehicles: note that the data provided in
Exhibits 1-7 and 1-8 does not include any breakout of heavy vehicles. Even
though the proportion of heavy vehicles is a required input to our
analysis, we sometimes find in the real world that not all the information
we need has been previously collected. One option would be to return to
the field to collect additional field data, but this can be expensive,
time-consuming, and outside the realm of practicality for some purposes.
In this case, we happen to know from our familiarity with the area that
truck volumes are negligible during the peak hour, and so it will be
reasonable to assume that there are no heavy vehicles (i.e.,
trucks, through buses, and large recreational vehicles) in the traffic stream. |
| The grade of all approaches is known to be
level, and so a 0% grade is assumed for each approach. The grade of an
approach has an effect on the critical gap for the movement. A downgrade
approach to the intersection reduces the critical gap because vehicles
accelerating from a stop have an easier time entering or passing through
the traffic stream. |
| The
peak hour factor
(PHF) is a measure of the
traffic demand fluctuations within
the peak hour. For this problem, we are assuming that a value of
1.0 for the peak hour factor is appropriate. This means that there is no
variation in the volume during the hour. In reality, field studies show
that the peak hour factor for this intersection is less than 1.0,
indicating that there is indeed a variation of traffic volumes across the
hour. We are using a value of 1.0 for the PHF because we are interested in
evaluating average conditions across the hour; in other situations
where the analyst is interested in evaluating conditions during the peak
15-minutes of the hour, then the field-observed value for the PHF should
be used. |
| The intersection has no median that vehicles from
the minor street can use as a refuge as they cross U.S. 95. The minor street approaches (Styner and Lauder) have no
storage (flared
approaches) at the stop line in which right turning vehicles can
by-pass through vehicles that are already waiting at the stop line. |
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