E18 motorway is one of Finland's most important international connections, linking the Scandinavian capitals together as well as with Russia and Europe.
The E18 (Highway 1) section between Muurla and Lohjanharju as a two-lane highway did not meet the alignment requirements for the traffic levels at that time. Now the entire stretch of road between Turku and Helsinki has been transformed into 4-lane motorway. The project was implemented using the Public Private Partnership model (PPP): design, construction and maintenance were provided by means of a single service agreement.
Pöyry designed seven twin tunnels, including Finland's longest (2,246 m) road tunnel, and 28 tunnel mouth structures, some of which also serve as bridges for roads crossing the motorway. The tunnels are designed with two meter high pre-cast concrete crash barriers throughout. Emergency exits linking the tunnels are situated at max 250 m intervals. Four tunnels are water and frost insulated throughout.