For a **passenger car towing a trailer** on a **conventional road**, the maximum permitted speed is **80 kilometers per hour**. This is because vehicles with trailers have specific speed restrictions on different types of roads.

- On **conventional roads**, the maximum speed for vehicles with trailers is **80 km/h**.
- This limitation is applied to ensure safety, as trailers can affect the stability and control of the vehicle.


Therefore, the correct answer is that the maximum permitted speed is **80 kilometers per hour**.