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 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.
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.
In 2014, the project won a Consulting Engineers South Africa, AON Engineering Excellence award, and a South African Institution of Civil Engineering National Project award for its innovative design and positive contribution to road safety.
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:
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.
Aurecon’s design process included: