Table of Contents

Appendix E 4.2 Analysis Results for Design 2

With the default actuated signal settings, an average cycle time of 138 seconds is estimated with displayed green times of 50 seconds each for Phases A and B, and 20 seconds for Phase C. This is the maximum cycle time that results from all critical movements requiring maximum green times.

The intersection performance under this set of timings (long cycle time) is not satisfactory as seen in Figure E 8. Although satisfactory performance is achieved for the right turn movement from North, all pedestrian movements and the right turn movements from other approaches are seen to experience long delays (levels of service F for pedestrians and E for those right turn movements).

Figure E 8: Average delay and level of service estimates for Design 2 (default maximum green settings)

Source: Akcelik and Associates (2009), ‘Intersection output provided by source’.

Figure E 9 indicates optimum cycle time solutions for Design 2. For cycle times in the range 70 to 140 seconds, delay is minimised at a cycle time of 75 seconds and capacity is maximised at a cycle time of 85 seconds. These solutions indicate satisfactory results for all movements (level of service D or better is obtained for all vehicle and pedestrian movements). Significant decreases in capacity with longer cycle times are due to the existence of short lanes, filter right turns and lane blockages (by left turns waiting for pedestrians, and filter right turns waiting for gaps).

Figure E 9: Average intersection delay and total effective capacity versus cycle time for Design 2

Source: Akcelik and Associates (2009), ‘Intersection output provided by source’.

Considering coordinated signal operations (on the basis that this is the critical intersection in the signal coordination area), a cycle time around 80 to 110 seconds would be acceptable for Design 2. Using 70% of default maximum green settings (35 seconds for through and left turn movements and 14 seconds for arrow-controlled right turn movements), a cycle time of 102 seconds is obtained with displayed green times of 35 seconds each for Phases A and B, and 14 seconds for Phase C. The performance results under these timings are generally satisfactory except level of service E for all pedestrian movements (average delay 44.2 seconds).

Given the above results, a cycle time of 90 seconds is specified for coordinated signal operation. Maximum green settings of 35 seconds for through and left turn movements and 14 seconds for the arrow-controlled right turn movement (70% of default values) are used. The resulting displayed green times are 30 seconds each for Phases A and B and 12 seconds for Phase C. The performance results under these timings are shown in Figure E 10 and Figure E 11. The largest degree of saturation is 0.77, average delay is 21.2 seconds for all vehicles (level of service C) and 38.3 seconds for all pedestrians (level of service D).

Figure E 10: Average delay and level of service estimates using a cycle time of 90 seconds for Design 2

Source: Akcelik and Associates (2009), ‘Intersection output provided by source’.

Figure E 11: Lane flow, capacity and performance results using a cycle time of 90 seconds for Design 2

Source: Akcelik and Associates (2009), ‘Intersection output provided by source’.

Finally, a design life analysis is carried out using the reduced maximum green settings (70% of default values). All demand flows are increased from current levels by applying a traffic growth rate of 2% per year for all movements (compound growth method used). Signal timings are calculated under each demand flow scenario. As seen in Figure E 12, the results indicate that the intersection would be operating at practical capacity after eight years. This means that traffic demand could increase by 17.2% before the intersection reaches the point when the spare capacity is zero, i.e. the intersection degree of saturation equals the practical (target) degree of saturation of 0.90.

Based on the above analysis results, it may be concluded that Design 2 provides a satisfactory solution to the problems experienced with Design 1. It is important to note that the performance of this design would deteriorate significantly if cycle times above 100 seconds resulted from the use of long maximum green settings.

Figure E 12: Average intersection delay and percentage spare capacity versus future years for Design 2 (with maximum green settings at 70% of default values)

Source: Akcelik and Associates (2009), ‘Intersection output provided by source’.