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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:

bulletTraffic 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.
bulletThe number of lanes and lane configuration for each approach can be determined from the aerial photograph.
bulletHeavy 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.
bulletThe 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.
bulletThe 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.
bulletThe 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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