Costain and joint venture partner Skanska has won a £15m contract to build the Royal Oak Portal, the first tunnel-related construction contract for London's Crossrail project.Work on the tunnel, near to Paddington main line station, will start straight away. It will act as the transition ramp for Crossrail trains when they enter and exit central London tunnels. The job is expected to finish in March next year."We are delighted to have been awarded this first tunnel related construction contract for Crossrail," said chief executive Andrew Wyllie. "To be involved in the Crossrail project is a significant step forward for Costain and a valuable addition to our strong rail portfolio."