Connecting people and places safely through the N4-8X upgrade, South Africa

The N4-8X is part of the N4 Toll Road, Maputo Development Corridor (MDC) operated by Trans African Concessions (TRAC).

Located near Malelane, Mpumalanga Province, the highway is a critical transport link between South Africa and Mozambique. High traffic volumes of up to 1,200 vehicles per hour had created significant congestion issues with the expected number of vehicles forecast to grow to almost 2,000 vehicles per hour by 2028.

Having worked with TRAC on previous upgrade projects along the N4 Toll Road, SMEC understood the client vision to connect people and places quickly, conveniently, and safely. The team set out to design a solution to replace the 15.5km two-lane carriageway with an undivided four-lane carriageway road of 16.4m surface width. To optimise widening of the road, geometry was carefully analysed to utilise the existing road alignment.

SMEC led the design and procurement phases of the project from inception to completion. Services included project management, geometric design, stormwater drainage design, hydrology, geotechnical engineering, electrical engineering, materials and pavement design, and structural engineering. The team also developed an access management plan, which facilitated the construction of formalised intersections and access roads.

Key features

Digital Design: The team modelled as much detail as possible in 3-D, right down to the pavement layer interfaces and the position of the guardrails. Horizontal and vertical best-fit alignments were created which enabled the team to seamlessly tie into existing infrastructure and optimise grading.
Access and Safety: A butterfly intersection has been introduced to ease right turn movements via a protected acceleration lane. Other features of the access management system include a bus turnaround facility, protected right-turn lanes and acceleration/deceleration tapers for local properties, filling stations and provincial road intersections. The scope also included a new sidewalk to accommodate pedestrian movements and a drop-and-go facility constructed for an adjacent primary school.
Infrastructure: Block paving at the Nkomazi Toll Plaza was replaced and 18 structures (bridges and major culverts) were widened to accommodate the upgraded road cross-section. Two filling stations and street lighting elements were relocated.
Contract Management: During construction the team introduced a Technical Query System was used to allow for formal communication between the contract administration team, the contractor, and the design team. The system assisted with clarification of any queries related to design and facilitated prompt resolution of technical queries during the construction phase.
Sustainability: The team adopted a reduce reuse approach to materials, such as reusing existing guardrails. Recycled blocks were used to construct a new sidewalk between Kaapmuiden Primary School (west of the toll plaza) and the community (east of the toll plaza). As part of the project SMEC’s engineering team also provided economic value through employment and skills transfer to local workers.

Timeline

2014: Preliminary Design
2018: Commencement of Detailed Design
2018: Completion of Tender Documentation
2019: Successful contractor appointed
2022: Project completed

Location

South Africa

Expertise

Roads & Highways Transport Planning & Advisory

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Key features

Timeline

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