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Problem 1 Discussion

ID# C1010D1

Problem 1: Discussion of the U.S. 95/Styner-Lauder Avenue Intersection

The analysis presented thus far using the HCM methodologies for Chapters 16 and 17, and the conclusions reached using these methodologies, all seem relatively straightforward. The delay for the minor movements at the TWSC intersection of U.S. 95/Styner-Lauder Avenue will continue to increase during the next ten years. Installing a signal at the intersection, while somewhat inconveniencing traffic on U.S. 95 that currently operates with no delay, will improve traffic operations. But have we taken a thorough look at the situation, or is there more to consider?

Yes, there is more to this story! We considered the U.S. 95/Styner-Lauder Avenue intersection as isolated in our initial analysis, but in reality, most intersections do not operate in isolation, and the U.S. 95/Styner-Lauder Avenue intersection is no exception.  

Let's consider what kind of a system this intersection is a part of. Review the sketch and aerial photograph to remind yourself of the geometric layout of the U.S. 95 corridor.


Sweet Avenue is located 1,070 feet to the north of Styner/Lauder. It is a signalized intersection and serves as a major entry point to the University of Idaho.

bulletPalouse River Drive is located 2,410 feet to the south of Styner/Lauder. It is currently a TWSC intersection but the Idaho Transportation Department is considering installing a signal at the intersection.

If we consider the U.S. 95/Styner-Lauder Avenue intersection to be a part of this arterial system, there are several new issues that must be considered in our analysis:


What are the arrival patterns at the U.S. 95/Styner-Lauder Avenue intersection of vehicles traveling southbound from the Sweet Avenue intersection? If Styner/Lauder is TWSC, and if the vehicles arrive in other than a random manner, the capacity that we computed earlier might underestimate the actual capacity.


If Styner/Lauder is signalized, the arrival rate and degree to which vehicles travel in platoons from Sweet Avenue and arrive during the green phase or the red phase has a direct impact on delay.


What quality of progression is possible if signals are installed at Styner/Lauder and at Palouse River Drive? Will it be possible to provide good vehicle progression if Styner/Lauder is signalized?

bulletWhat effect will the signalization of Palouse River Drive have on the operation of Styner/Lauder (effect of arrival patterns as discussed above) and on the arterial as a whole?

How would you re-cast the problem that you first considered, based on the issues listed above? Take a few minutes to summarize how you would revise the original problem statement.

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