Traffic Impact Assessment

2.8     Intersection Operations

        2.8.1 Intersection Assessment Parameters

        A series of SIDRA analyses were conducted to quantify the existing traffic operations at the above
        intersections. The analyses were based on the traffic count data presented in Appendix B with:

                 Peak Flow Factors (PFF), as detailed in Table 2.4
                 the observed proportion of heavy vehicles (%HV) for each movement
                 SIDRA default values for other parameters

        The results are presented in terms of the degree of saturation (DOS), 95th percentile vehicle queues,
        and critical movement at each intersection. The degree of saturation for a movement is defined as
        the ratio of traffic demand to the capacity of the movement. The critical movement relates to the
        approach or movement with the highest degree of saturation. Table 2.4 is an extract from the
        SIDRA manual and defines the operational rating and level of service for all intersection types.

        Table 2.4:            SIDRA INTERSECTION RATINGS

            LEVEL OF                                           DEGREE OF SATURATION
             SERVICE                      SIGNALS                       ROUNDABOUT          PRIORITY
                LOS A                       x ≤ 60%                            x ≤ 60%       x ≤ 60%
                LOS B                  60% < x ≤ 70%                      60% < x ≤ 70%   60% < x ≤ 70%
                LOS C                  70% < x ≤ 90%                      70% < x ≤ 85%   70% < x ≤ 80%
                LOS D                  90% < x ≤ 95%                      85% < x ≤ 95%   80% < x ≤ 90%
                LOS E                 95% < x ≤ 100%                     95% < x ≤ 100%   90% < x ≤ 100%
                LOS F                      100% < x                            100% < x      100% < x


        2.8.2 Cooroy Belli Creek Road / School Access

        The existing Cooroy Belli Creek Road / School Access priority-controlled intersection layout and
        equivalent SIDRA representation are shown in Figure 2.5. There is sufficient width on the school
        access for a left-turning vehicle to pass a right-turning vehicle stopped at the stop line. Therefore,
        the intersection has been modelled with a short left-turn lane on the school access.

        The results of the intersection analyses are summarised in Table 2.5 and included in Appendix C.
        The results indicate that the intersection currently experiences LOS A operations under existing
        weekday morning and afternoon peak hour conditions.




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