The M55 Consortium, led by Mott MacDonald, conducted a feasibility study on behalf of the Operating Company Amsterdam Almere (WAA). The solution, the M55-IJmeerlijn, is a metro connection between Amsterdam and the outlying city of Almere via an immersed tunnel under a large lake, the ‘IJmeer’. The feasibility design for the new M55 metro utilises the existing metro infrastructure in Amsterdam including spare capacity, follows the shortest possible route, uses lightweight rolling stock and is therefore highly efficient and cost effective. It represents a 40% saving on projected construction cost compared to the reference design while enabling a higher frequency service – 16 metros per hour in each direction in the rush hour; a fast, attractive and reliable public transport system. Mott MacDonald was supported in the M55 Consortium by MNO Vervat, HTM Consultancy, Project & Proces Consultancy, EconoVision, Balancia, BACA Architects and Zwarts & Jansma Architects.