Oneways

Oneways are mapped by simply adding a oneway=yes tag to the road’s way. Keep in mind that ways have a directionality. So the road will be a oneway in the direction of the way. If you need to change the flow of the one way, you have two options:

• Change the direction of the way (Tool > Revers ways in JOSM or the << context icon on iD)
• Or tag with oneway=-1 - use this approach where the way’s directionality already governs another attribute such as bus route.

OpenStreetMap Wiki: Key:oneway