Sub-problem 4a: Northbound Left-Turn Capacity

The logical conclusion to draw from the graph on the preceding page is that the minor street conflicting movement volume is too heavy to permit a viable TWSC operation at this intersection. Without going into the numbers in any greater detail, the graphical presentation indicates that the demand volume is considerably higher than the capacity. Keeping in mind that the potential capacity for a movement does not consider the competition from other movements at the same priority level, it will generally represent an optimistic assessment of the capacity. When even this optimistic assessment fails, you would conclude that there is no point in proceeding any further with the investigation of TWSC.

Normally you would stop at this point and look at some other control alternatives. We will, however, carry the TWSC concept into a couple of other sub-problems to illustrate some features of the HCM analysis procedure and to set the stage for the consideration of other alternatives.