To cater for the construction of a grade-separated interchange as part of State Highway 20 Mt Roskill Motorway extension project, an innovative solution was developed and implemented by combining two conventional intersection types. New Zealand's first fully signalised roundabout Hillsborough Ring Road was constructed at the intersection of State Highway 20 and Hillsborough Road. Due to high and unbalanced traffic flows in the morning and afternoon peaks, roundabout signalisation was considered necessary. The need to address safety concerns and to cater for an at-grade haul crossing, pedestrian facilities and site accesses led to the signalisation of all the approaches to the roundabout. Innovative traffic signal system design allows traffic to flow through the roundabout with minimal stoppage. The vehicle stream entering the roundabout follows an anticlockwise sequence, whereby the signal start up and cut off losses are minimised. Despite some undesirable driver behaviours, the Ring Road has operated safely and effectively as an intersection replacement. The ease to switch the traffic over to new motorway alignments also demonstrates the versatility of the Ring Road for temporary traffic management. The Ring Road, a signalised roundabout, is an excellent traffic engineering solution for balancing the operational performance of all approaches and improving traffic safety for all the road users. (a).
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