Further Advice Response 21-8-24 Attachment 2 - Site Distance Correspondence

SISD is calculated using the formula:

                                             𝐷𝑇 × 𝑉            𝑉2
                                    𝑆𝐼𝑆𝐷 =          +
                                              3.6     254 × (𝑑 + 0.01 × 𝑎)
where:
𝐷𝑇 = decision time
    = 𝑅𝑇 + 𝑂𝑇
𝑅𝑇 = reaction time
    = 2.0 sec (general minimum)
𝑂𝑇 = observation time
    = 3.0 sec
V   = design speed
    = 60km/h (as discussed)
d   = coefficient of deceleration
    = 0.36 (normal maximum)
a   = longitudinal grade

Using the Normal Design Domain (NDD) parameter values outlined above, the required Safe Intersection Sight
Distance (SISD) is 123m for the eastbound approach (based on 0% average grade) and 124m for the westbound
approach (based on -0.9% average grade). The SISD Sight Distance drawing is enclosed as Appendix B.

Minimum Gap Sight Distance (MGSD)

AGRD4A-23 defines MGSD as the distance corresponding to the critical acceptance gap that drivers are
prepared to accept when undertaking a crossing or turning manoeuvre at intersections. It is measured from
the point of conflict (between approaching and entering vehicles) back along the centre of the travel lane of
the approaching vehicle. The drivers eye height is 1.1m and the object height is 0.65m above the travelled way
(a vehicle indicator light).

MGSD is calculated using the formula:
                                                              𝑉
                                               𝑀𝐺𝑆𝐷 = 𝑡𝑐 ×
                                                             3.6
where tc is the critical acceptance gap.

According to Table 3.5 of AGRD4A-23, the critical acceptance gap for both left-turn and right-turn movements
from a minor road onto a two-lane, two-way road such as Lake Cooroibah Road is five (5) seconds. Based on
the adopted design speed of 60km/h, the minimum gap sight distance requirement is 83m.

Sight Distance Assessment

The available SISD and MGSD at the existing site access driveway meets the Normal Design Domain (NDD)
requirements. The results are summarised in Table 1 below.




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