Cars are loaded on the railway wagon for the railway shuttle at any of the three stations, Karis, Lemland or Kapellskär. At specific time the shuttle start for the other end and the car is offloaded, and the journey can continue. The plan is to achieve almost the same service level a road tunnel under the sea and the archipelago would provide.
An interesting note about this, is that road E18 should follow this proposed railway link and not the ferry lines of today. By redesigning E18 it will be easier to drive from Helsinki towards Stockholm (see European route E18 )