The **maximum speed** allowed for a **motorcycle towing a trailer** on an **urban road** is **50 km per hour**. This is because, in general, motorcycles must adhere to the speed limits established for urban roads, which are **50 km/h** on streets with multiple lanes in each direction.

Additionally, vehicles carrying loads, such as a trailer, must follow the same speed regulations as other vehicles in the city, unless otherwise indicated. There are no specific mentions in the texts about an additional speed reduction for motorcycles with trailers on urban roads, so the standard limit of 50 km/h applies.