Instructions for building bridges, tunnels and overpasses in Cities: Skylines

The transportation system is a core part of Cities: Skylines. Players must know how to regulate traffic so that all vehicles are always moving and avoid congestion that delays everything. Traffic jams can prevent goods from being delivered to an industrial or commercial building, and prevent residents from getting to their workplaces on time.

If traffic congestion becomes severe, these problems can cause people to abandon an area. Part of building a good road network includes learning how to build bridges, overpasses and tunnels in the right locations to connect roads, while avoiding intersections.

Here it is how to build streets, including tunnels and overpasses in Cities: Skylines.

Things to know about bridges and tunnels in Cities: Skylines

The first thing players need to know is that bridges and tunnels do not have their own sub-menus or categories in Cities: Skylines. This is because the game will automatically build these structures based on where the player draws the line and how high they build them. If a road crosses a lake or river, Cities: Skylines will add piers. If a road is raised above the ground, the game will add support pillars. If the player lowers the height of the road below ground level, the game will construct a tunnel entrance or exit. This also applies to metro and railway tracks.

Of course, Cities: Skylines players should also remember that bridges and tunnels are much more expensive than surface roads, and the game will track this price even if the player isn’t paying attention. A simple two-lane road 10 spaces long costs 400, but that number increases to 1040 for a bridge ramp and 2400 for a tunnel entrance. Another point to note is that the game will not allow roads to be too steep: a 1-cell high slope must be at least 6 cells long, and a 2-cell high slope must be 12 cells long.

Another important factor is overlap. When players build a road that changes elevation, Cities: Skylines will add an elevation change to the end of the road regardless of its length. This means the player needs to build a ramp before being able to build a bridge over another road or building.

Tips for connecting crowded roads

• When it comes to motorway connections, players should use the shortest possible corners. The sharper the corner, the more vehicles have to slow down to get through, and when vehicles slow down on the highway, they can cause serious traffic congestion.
• Even after players build ramps at the correct height to avoid other paths, their bridge may still encounter the warning “Space has been taken up!“. This happens when the pillars supporting the road are too close to the objects below. Players can still build overpasses across the road, but they will have to change the connection angle, change the road length, or possibly take a different route to get across.
• Some of the best mods for Cities: Skylines allow players to choose specific connections for each road intersection, adjust the length and curvature of existing roads, and even bypass issues like bridge abutment collisions. However, none of these features were present in the original game.
• Players should focus on using bridges, skyways, and overpasses rather than tunnels, as these structures are much more expensive.
• Upgrading overpasses is very difficult because each upgrade can change both the road width and the size of the supporting pillars. Players may need to delete parts of the overpass and rebuild it according to the upgraded version.
• Power lines follow the same rules as roads when intersecting other roads and structures. However, power lines can pass above ground lines without having to go higher and without bending. They also cannot go underground.
• Players who want to design more realistic highway connections can use the landscaping tool to build a pair of hills on either side of the highway. This tool does not allow the player to adjust the height of the highway, so the edges of the hills will be sharp. That allows players to build a short bridge that spans just the highway and can be much less expensive than a long bridge.
• Although the player cannot change the height of the bridge, they can use the landscaping tool to bury the bridge’s support pillars and make it look like a road above ground. However, it will still be a bridge and any suspended structures or trusses will still be there.