Sub-problem 2a: Analysis of the Existing TWSC Intersection Considering the Effects of the Adjacent Intersections

Exhibit 1-22 shows a plot of capacity for the EB through and right turn movement at the U.S. 95/Styner-Lauder intersection as a function of the distance away from an upstream signalized intersection. The last point on the right of Exhibit 1-22 shows a capacity of 329 veh/hr for a distance of 1,070 feet, which is the distance between Sweet Avenue and Styner-Lauder (Dataset). In fact, we can see that for any distance greater than about 600 feet, there is no capacity increase.

But when we get closer than 600 feet to the signalized intersection, the platooning begins to have an effect on the capacity of this movement. At 250 feet from the intersection, the capacity increases by 20 percent to 396 veh/hr. The delay is also reduced by 20 percent, from 25 sec/veh to 20 sec/veh.

So, while there may be some effect of upstream signals in some situations, this effect does not show up in this particular problem. It is important to point out that the method we've just used from the HCM to account for the effect of upstream signals is an approximation. Where the effect of the upstream signals is more important to the final result than in this example, other techniques are available for estimating this effect. These techniques are more microscopic, require more input data and effort to apply, but may not give any more accurate answer, unless more refined data is provided. They can, however, provide further insight and are warranted for use in some situations.

We will next consider, in sub-problem 2b, whether arrival patterns of Sweet Avenue vehicles have an effect on the Styner-Lauder intersection if the latter intersection were to be signalized.