Problem 2: Analysis

It is now useful to bring together the results of the three sub-problems that we considered as part of problem 2. In this problem, we considered the question of whether or not to signalize U.S. 95/Styner-Lauder Avenue not as an isolated one, in which we look at only the conditions at the intersection, but rather in the context of the U.S. 95 arterial and the intersections adjacent to Styner-Lauder. 

We learned in sub-problem 2a that the flow patterns from the adjacent intersections (specifically Sweet Avenue) do not affect the capacity of the Styner-Lauder Avenue intersection when it is operating with stop-sign control. The distance between Sweet Avenue and Styner-Lauder is great enough that the platoons from Sweet Avenue have dispersed sufficiently so that the capacities of the Styner-Lauder approaches are not affected.

We learned in sub-problem 2b that if the intersection of Styner-Lauder were signalized, there would be some effect on the delay of the U.S. 95 traffic at the intersection. This reduction in delay over the conditions that we considered in problem 1 results from the degree of coordination that can be achieved between the Sweet Avenue and Styner-Lauder Avenue intersections.

Both results continue to leave open the opportunity to signalize the Styner-Lauder intersection.

We found in sub-problem 2c, however, that when we apply the HCM urban street methodology, the benefits to the side streets (Styner and Lauder approaches) must be traded off against a reduction in level of service along the U.S. 95 arterial. The level of service before Styner-Lauder is signalized is estimated to be B. After the signal is installed, even with the seemingly acceptable delay to U.S. 95 traffic, the level of service for this arterial segment would be reduced to C, because the travel speed on the arterial is reduced from 29 mi/hr to 25 mi/hr.

There are other ways to minimize the impacts of a new signal on arterial operations and the through-traffic travel times. One of these ways is to coordinate the system of signalized intersections within the arterial section, and the effect of this was demonstrated in sub-problem 2d. It is also possible to minimize these impacts by restricting the non-arterial green time at the new Styner-Lauder/U.S. 95 traffic signal. A methodology for accomplishing this latter approach is further discussed in Problem 4.