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

How can you compare the delay at an unsignalized intersection and a signal? In these comparisons, you can see that a signal imposes delay (zero in TWSC) on the major street through and right-turn movements, which are also the movements with the highest volumes. 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 in seconds 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 compare total delay in seconds applied to all vehicles. This requires that we apply the computed delay in seconds per vehicle to the number of vehicles traveling through the intersection for both the signalized and TWSC intersection scenarios. This comparison is illustrated below:

Table 8. Projected Museum at Reitz comparing TWSC and Signal Control
	EB			WB			NB			SB
	L	T	R	L	T	R	L	T	R	L	T	R
Volume	379	670	2	0	597	178	12	0	8	204	0	484
Delay TWSC	30.4	0	0	10.2	0	0	999	0	999	999	0	999
Delay Signal	584.6	17.8	17.8	10.4	24.2	24.2	27.3	0	27.3	35.5	0	286.5
Total Delay TWSC	11,522			0			19,980			687,312
Total Delay Signal	148,941			19,065			546			157,896
Intersection Delay	TWSC		718,814		Signal		326,448		Difference		392,366 (55%)

As you can see, for existing geometry and projected traffic, the signalized intersection actually performs better (less delay) than under TWSC. Since the delays were very large on the minor street movements under TWSC, values of 999 seconds per vehicle were assumed, when the delay equation actually predicts even larger values. 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 computed for the side street movements make this case somewhat unique.

Table 8. Projected Museum at Reitz comparing TWSC and Signal Control