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.

[ Back ] [ Continue ] to Sub-Problem 5c