6.12.2 Paired Intersections
‘Paired intersection’ is a term used for two closely spaced intersections with limited queuing space between the intersections (i.e. internal approaches). Typical examples are staggered T‑intersections and freeway diamond interchanges, as shown in Figure 6.22(a) and (b). Intersections with a wide median have similar characteristics.
Paired intersections are regulated by either a single traffic signal controller using built-in offset arrangements achieved through special phasing arrangements, or by two separate signal controllers that are linked under a coordination signal system.
Paired intersections may use an early cut-off green period, to allow an upstream signal to be terminated earlier than a downstream signal in order to minimise queuing on internal approaches. For additional guidance on this type of operation, refer to Appendix G.4.5.
Severe unequal lane utilisation may be observed due to heavy origin-destination flows in paired intersection systems, e.g. ‘dog-leg’ movements at staggered T-intersections. This should be taken into account in designing geometry and signal phasing for paired intersections.
Management of queuing in internal approaches of a paired intersection system is important to avoid blockage of upstream signals by through and turning vehicles queued in internal approach lanes. Early cut-off and early start phasing arrangements, simultaneous offsets and shorter signal cycle times are useful methods for this purpose.
It is important to ensure that adequate queue storage spaces are provided for vehicles turning right from internal approaches to freeway entry ramps.
With paired intersections, care should be taken to avoid the potential ‘see through’ problem, i.e. downstream green signals being seen by motorists stopped at the upstream stop line (refer to Part 10 of the Guide to Traffic Management, Austroads 2019d).
For key traffic management selection considerations for staggered T-intersections and freeway interchange ramps, refer to Part 6 of the Guide to Traffic Management (Austroads 2019c)..