One could argue that Cities: Skylines is a road and traffic simulator first and a city simulator second. After all, the road-building tools are very intricate and detailed, and it's so easy to build custom roads that players have recreated cities from real life and from other games.
However, to get that far, players of Cities: Skylines first need to master the basics. This includes knowing how to set down one-way roads and get them to point in the right direction. The way to do this depends on whether players are creating a new road or upgrading an existing road.
New Road Construction
To build a new one-way road, players must first choose a one-way road option from the road build menu. Most of the road tabs have one-way options even during the early game, but players will have to click the arrows next to the road selections to see them.
The way the game decides which way the road should go initially is by checking where the road begins and ends. Simply put, the road goes in the same direction the player moves their cursor in. To reverse the road direction, simply cancel the construction and start again from the old endpoint. This can be inconvenient if players are trying to curve a road in a very precise way, but fortunately, there's also a way players can change the direction of existing one-way roads.
Road Upgrades
Cities: Skylines has a very robust road upgrade system. While in the road menu, check the options to the left of the road selections. One of them is an exclamation point, and while this option is active, players will change a highlighted road segment into whichever road is currently selected. Players can use this tool to change the number of lanes, the road decorations, the road width, or whether a road is two-way or one-way.
Players can't choose which direction a new one-way road goes in, but they can switch the direction of an existing one-way road. The way to do this is to hit the rotate button (which is the right mouse button on PC).
Swapping road directions like this in Cities: Skylines doesn't cost any money, so players are free to do so as much as they like. Just remember to check that every segment of a one-way road points in the same direction because otherwise, it will become impossible for vehicles to travel down.
Cities: Skylines is available now on PC, PS4, Switch, and Xbox One, and it's coming to PS5 and Xbox Series X/S on February 15.