Easing extreme congestion with a new kind of interchange
As commuters use the new KwaMashu Interchange in South Africa, they know that extreme congestion throughout the day and long vehicle queues are a thing of the past. Aurecon’s pioneering conversion of the standard diamond KwaMashu Interchange to an innovative diverging diamond layout has provided a low-cost, effective means of enhancing the capacity and safety of the interchange.
It is the first application of a diverging diamond interchange in the Southern Hemisphere, that is also on a left-hand drive road system. It was SANRAL, Aurecon’s client, who was bold enough to adopt Aurecon’s concept of a diverging diamond interchange when it had never been done before in the area.
The status quo
The original KwaMashu Interchange carried high volumes of traffic in all directions, resulting in high levels of congestion. Traffic queues extended onto the N2 northbound carriageway for several kilometres during high peak periods. These delays caused frustration among commuters. The delays also led to increased accident rates at the interchange.
Extensive research and analysis of the existing interchange and the surrounding land confirmed that the KwaMashu Interchange could be converted to a diverging diamond interchange. SANRAL used this opportunity to implement the diverging diamond interchange as a pilot project to test its use on South African freeways and for South African driving conditions.
The first of its kind
When it was commissioned the KwaMashu Interchange was the first application of a diverging diamond interchange in the Southern Hemisphere, and for left-hand drive.
The diverging diamond interchange was innovative because the traffic flows in the two directions of the cross-road (non-freeway) on the opposite (right-hand) side of the roadway, between the two interchange intersections.
Vehicles on an overpass or underpass briefly cross over lanes at a two-phase signalised intersection to drive on the ‘wrong’ side of the road, allowing free and unopposed right and left turns to and from the freeway. After crossing over or under the freeway, the vehicles return to their normal left-hand lane.
KwaMashu Interchange realised the following advantages for commuters:
Capacity increased by more than 15 per cent
Delays through the interchanged reduced by up to 60 per cent
Construction time reduced by 50 per cent compared to a traditional interchange design
Construction costs were significantly less
Traffic and pedestrian conflict points were greatly reduced
Right-angled accidents were eliminated
The reduction in queue back-ups had a beneficial impact on lowering pollution in the area by reducing carbon outputs
Extensive planning went into the decision to design and construct a diverging diamond interchange including extensive traffic studies. This was followed by a sophisticated assessment of key geometric elements of the proposed layout to determine the suitability of the interchange for conversion to a diverging diamond interchange.