Stockholm is at the junction of the European routes E4, E18 and E20. A half-completed motorway ring road exists on the south, west and north sides of the City Centre. The northern section of the ring road, Norra Länken, opened for traffic in 2015 while the final subsea eastern section is being discussed as a future project. A bypass motorway for traffic between Northern and Southern Sweden, Förbifart Stockholm, is being built. The many islands and waterways make extensions of the road system both complicated and expensive, and new motorways are often built as systems of tunnels and bridges.