Buoys and Boat

Loch Lomond Shores, Balloch

On UK roads, speed limits are still posted in miles per hour (mph) —a legacy of imperial units enshrined in legislation like the Road Traffic Regulation Act 1984. Despite broader metrication, road signs remain resolutely imperial.

But on waterways, especially inland lochs like Loch Lomond, the story shifts. Boat speed limits are often posted in kilometres per hour (kph). This reflects:

Maritime and inland waterway conventions, which lean more heavily on metric units across Europe.

Safety signage managed by local authorities or national park bodies, who may adopt metric for consistency with boating regulations and international visitors.

Loch Lomond & The Trossachs National Park Authority, for instance, uses kph on its boating signs—e.g., 11 kph ( approximately 7 mph) in certain zones.

It’s a curious duality: mph on land, kph on water