**Single carriageway roads** can have **two-way traffic**. This means that on the same road, vehicles can travel in opposite directions, each in its own lane.

- **Two-way roads**: On these roads, one lane is used to go in one direction and the other to return. This is common on many roads, both urban and interurban.

- **Lanes in the opposite direction to the usual**: Sometimes, lanes are enabled in the opposite direction to the normal to improve traffic flow or during roadworks. This allows vehicles to travel in both directions on a single carriageway, provided certain precautions are followed, such as keeping the lights on and respecting speed limits.

Therefore, it is possible for a single carriageway road to have traffic in both directions, which confirms that the correct answer is **"Yes"**.