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Analysis - Page 2 of 2

ID# C1010A2

Problem 1: Analysis of the U.S. 95/Styner-Lauder Avenue Intersection

Exhibit 1-19. Summary comparison of average control delay estimates (sec/veh)

Movement

Existing volumes

Future volumes

TWSC

Signal control

TWSC

Signal control

EB LT

47.0

19.1

297.5

21.2

EB TH/RT

25.3

20.7

55.7

22.0

WB LT

36.0

18.9

134.4

19.7

WB TH/RT

27.6

22.9

80.9

25.3

NB LT

8.6

5.7

9.1

5.9

NB TH/RT

 

6.1

 

6.3

SB LT

8.3

5.9

8.6

6.2

SB TH/RT

 

6.6

 

6.9

A review of the information contained in Exhibit 1-19 provides important information to think about as the decision to signalize the intersection (or not) is considered:

bullet

Drivers on U.S. 95 will experience some delay if signal control is added to the intersection, though the delay is minor (between 6 and 7 seconds per vehicle). However, more costly than this delay is the fact that some portion of the drivers on these approaches will have to stop, something that might be viewed as a degradation of service by many drivers.

bullet

This reallocation of delay, however, significantly improves the operations of the Styner (westbound) and Lauder (eastbound) approaches. For example, drivers will experience a slight improvement in their level of service (with average delay reduced from 27.6 seconds to 22.9 seconds) if the intersection is signalized with existing volumes. Considering operations with future volumes, this change is much more dramatic, with delay being reduced from 80.9 seconds to 25.3 seconds.

bullet

It is also important to point out that we should consider that the off peak period constitutes 80 to 90 percent of the total time that an intersection operates. During these times when volumes are often significantly lower than in the peak period, a traffic signal can sometimes be less efficient than stop-sign control. Or, a signal may not even be necessary during these time periods! This is why other forms of control (such as roundabouts) or flashing signals are sometimes considered during off-peak periods.

bulletOther options might also be available to avoid signalizing the intersection. If, for example, the signalized intersections on either side of the Styner/Lauder intersection are coordinated and timed in such a way as to create regular gaps in the traffic stream on U.S. 95, then the TWSC intersection analysis might yield much more acceptable results when these effects are taken into account. This may or may not be a practical option, but is something that should be considered so that decision makers are presented with the fullest-possible range of viable options.
The information presented here indicates that changing from TWSC to signal control will improve the operation of this intersection, particularly over the next ten years. The uncertainty analysis that we conducted as part of sub-problem 1c confirms that this decision is a sound one.

Discussion:
But have we considered all relevant factors in this analysis? Take a few minutes to identify other factors that you think should be considered in this analysis, and continue to the next page when you are ready.

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