Corbais Inaugurates Wallonia’s First Diamond Interchange
Wallonia’s first diamond interchange opened in Mont-Saint-Guibert. The 35 million euro infrastructure project aims to eliminate traffic bottlenecks, improve regional mobility, and enhance safety at a critical commercial crossroads connecting the E411 highway and the N25 axis.
The Bottom Line
- Total Capital Expenditure: The project cost 35 million euros, backed by a 32 million euro investment from project owner Sofico and 3 million euros from inBW via a Sowafinal regional funding mechanism.
- Capacity Relief: Designed to streamline transit for approximately 70,000 daily vehicles passing through the former “Planche à voile” intersection, cutting down collision points by half compared to standard highway layouts.
- Execution Metrics: Built by contractor TRBA following studies by the SBE bureau and supervision by SPW Mobilité et Infrastructures, the project was completed on schedule without delays.
Financing Structure and Regional Stakeholders
The capital expenditure for the interchange breaks down across distinct regional entities. The primary financing stems from Sofico as the project owner, allocating 32 million euros. An additional 3 million euros was deployed by inBW through the Walloon Region’s “Sowafinal” program, targeted specifically at civil engineering works and infrastructure connecting the local science park.
The project execution was managed by SPW Mobilité et Infrastructures alongside technical partner Sofico. Engineering studies were conducted by the SBE bureau, while actual construction was awarded to TRBA. Despite the complex operating environment, the contractor completed the build without schedule slippage, aided by favorable weather conditions. After the vegetation was cut a few months prior, the first shovel strokes were delivered in September 2023.
Traffic Fluidity and Engineering Mechanics
The interchange earns its “diamond” designation from its geometric rhombus layout, engineered explicitly to manage high-volume intersections featuring heavy left-turn demand. The design deploys a double underpass paired with synchronized surface traffic lights. This configuration allows opposing left-turn movements to occur simultaneously without crossing paths. Here, from now on, the left-turn flows are conducted simultaneously and without conflict.
| Project Metric | Figure / Detail |
|---|---|
| Total Investment | 35 Million Euros |
| Sofico Allocation | 32 Million Euros |
| inBW / Sowafinal Allocation | 3 Million Euros |
| Daily Traffic Volume | ~70,000 Vehicles |
| Carpool Parking Capacity | 145 Spaces (4 PMR) |
Approximately half of the 70,000 vehicles traversing this central economic hub of Walloon Brabant utilize the N25 axis. Consequently, there will no longer be a single intersection for users coming from the N25 and heading toward Brussels or Namur, and vice-versa. The new traffic management framework prevents queue backups from spilling onto the E411 highway. Furthermore, the construction incorporates active mobility solutions, featuring dedicated cycling lanes and a newly established carpooling parking facility containing 145 spaces, including four reserved for individuals with reduced mobility.
Economic Integration and Official Inauguration
The inauguration took place on a Friday in late morning, in the presence of all stakeholders and the mayors of the three impacted municipalities. Representing François Desquesnes, Minister of Spatial Planning, Mobility, Public Works and Local Authorities—who was occupied by budgetary negotiations—Vincent Blondel emphasized the strategic upside of the infrastructure.
Local authorities and project stakeholders agree that the diamond interchange acts as a vital catalyst for commercial expansion within Walloon Brabant. In terms of safety, a diamond interchange divides the risk of conflict points between users by two compared to a conventional highway interchange. By cutting the risk of conflict points between motorists in half compared to conventional highway exchanges, the development secures smoother logistics chains for the adjacent science park and surrounding industrial zones.
