**Sub-problem 5b:
**Three-phase
Traffic Signal Control with a Protected Westbound Left Turn

**The Minimum Delay Strategy
**

The final strategy
mentioned in the HCM is that of minimizing the sum of the delays to all
vehicles entering the intersection. This strategy seeks an optimal solution
instead of an equitable solution to the design of the signal timing plan.
The overall intersection delay shown in
Exhibit 3-39 was 24.5 sec/vehicle for
the equal v/c strategy, compared to 42 sec/vehicle for the equal delay
strategy. It is this performance measure that we seek to minimize.

The minimum delay strategy
also requires an iterative process that can be implemented either with
available software or by trial and error. It is common practice to start
this process using the equal v/c strategy as an initial solution. Following
this practice, it was found that the equal v/c solution could not be
improved upon by redistributing the green times. In other words, it was not
possible to lower the overall intersection delay below 24.5 sec/vehicle. So
we must conclude that the equal v/c solution in this case was also the
minimum delay solution.

While this outcome
should not be interpreted as a general signal timing principle, it will be
found that the outcomes of these two strategies are frequently not far apart
at isolated intersections, such as the one in question. Delay minimization is
a more important strategy in coordinated systems where other design
parameters related to the quality of progression between intersections must
be optimized.