Sub-problem 1b: Analysis of the Signalized Intersection with Projected Traffic

How can the delay at an unsignalized intersection be compared with that at a signal? These findings confirm the obvious, which is that a signal imposes delay on the major street through and right-turn movements, which would not have experienced these delays if the intersection were to remain under two-way stop control. The findings go beyond this to quantify the amount of delay likely to be experienced by these major street movements. This is an important consideration, since these are also the highest-volume movements at the intersection. On the other hand, delays are reduced substantially for all minor street movements. So, which case really represents the better control strategy, in terms of minimizing delay, for the overall intersection?

To better understand whether this is really an improvement to the operation of the intersection, at least as defined by levels of delay, we must realize that these delay values are expressed in terms of the average number of seconds of delay per vehicle. So, for comparison purposes, it is important to apply these estimates to the number of vehicles affected for each movement. To accomplish this, we can compute the total delay, in seconds, incurred by all entering vehicles. This requires that we multiply the computed average delays for each movement by the number of vehicles in each movement, and that we perform this calculation for both the signalized and TWSC intersection scenarios. This comparison is illustrated below:

As you can see, for existing geometry and projected traffic, the intersection actually performs better (less delay) under signalized control than under TWSC control. Since the delays were very large on the minor street movements under TWSC, values of 999 seconds per vehicle were assumed (the delay equation actually predicts even larger values than this). Even with this assumption, the delays on the minor street are reduced significantly with signal control. The delays do increase for the major street movements under signal control but are far outweighed by the improvements on the minor street approaches.

It should be noted that normally for undersaturated conditions, the benefit of zero delay for the major street throughs and rights would outweigh the benefit to side street traffic in this comparison. However, the very long delays estimated for the side street movements under TWSC control are what determined the outcome of this comparison.