Which regulation can you break on a motorway according to the provided text?

Stopping on the carriageway is considered a serious violation on a motorway, as it poses significant risks to both the person in the vehicle and other road users. Motorways are designed for the continuous flow of traffic, and stopping can lead to accidents or traffic disruptions. However, there are specific circumstances, such as an emergency or vehicle breakdown, where stopping may be necessary, but even then, it must be done safely and with caution.

On the other hand, the other options represent clear violations that are generally not acceptable in any situation. Overtaking on the hard shoulder is prohibited unless under specific emergency conditions. Using a bus lane improperly can result in penalties, as these lanes are reserved for public transport during designated hours. Driving without a seatbelt is a breach of safety regulations that can lead to severe consequences for the driver and passengers, as seatbelts are critical for protection. Therefore, stopping on the carriageway, while typically a violation, can sometimes be the least penalized under certain emergency conditions, making it the focus in this context.