Navigation transit markers

Navigation Transit Markers are posts placed alongside a navigation to allow powered craft to check their speed.

Examples of these markers can be found at several locations along the River Thames in England.

A navigation marker consists of a black and white ringed pole surmounted by a red open triangle.

For a craft to be within the speed limit, it should take a minute or more to reach the second pair of markers after passing the first pair of markers.

On the upper reaches of the Thames, the speed limit is 8 km per hour or 133.3 m per minute, and so the markers are set 133.3 m apart.

Principle of using navigation transit markers to check speed
Pair of markers at Kingston