Sub-problem 1a: Analysis of the existing TWSC intersection

Following are other points to consider regarding the required data:

• 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.
• We are assuming that there are no heavy vehicles (i.e., trucks, through buses, and large recreational vehicles) in the traffic stream and that all approaches to the intersection are level.
• We are assuming that there are no pedestrians crossing at the intersection, impeding the flow of vehicles.
• 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.

What default values should be used? Driver behavior at a TWSC intersection is described by two parameters, the critical gap and the follow up time. The HCM provides default values that represent average values from a number of measurements made at sites throughout the United States for critical gap and follow up time. However, conditions at the site (unusual geometric features, high volumes causing more aggressive driver behavior) that you are studying may produce values that are different than these default values. It is always better to use values that are estimated from the site that you are studying, if these values can be measured.

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