Sub-problem 1c: Analysis of Future Conditions

Uncertainty analysis is often used to consider the effects that uncertainty in the input values for a problem will have on the outputs, and whether these effects will be significant. To illustrate this kind of analysis, we will consider three cases. The first case is the base case, where we assume that the volumes that we used are correct. The second case assumes that our volume forecasts are high by 25 percent, while the third case assumes that the volume forecasts are low by 25 percent. Exhibit 1-14 focuses exclusively on a single performance measure (average control delay), though in reality we would also want to explore the impact on other performance measures such as v/c ratio and queue length.

Exhibit 1-14 shows two very interesting points. First, for the minor movements at the TWSC intersection, the volume changes have a large impact on the final results. This shows that the projected operation of the intersection is unstable to begin with, and that any increase in the volumes will further degrade the intersection performance. Second, we can have some degree of confidence that, under signal control, the intersection will perform as planned, even if we are somewhat uncertain about the input volumes that we've projected. These results can help decision-makers feel more certain about the range of possible ramifications associated with different control decisions.

In addition to varying the input volumes, we could also determine the sensitivity of other input or default values on the final results. For example, the critical gap, the follow up time, the saturation flow rate, and the arrival type are all important parameters in the computation of capacity and delay. The base case values for these parameters could also be varied to determine their effect on the final results.