Navigation Transit Markers are posts placed alongside a navigation to allow powered craft to check their speed. There are examples along the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 in England.

A navigation marker consists of a black and white ringed pole surmounted by a red open triangle. The configuration of the markers is made up of two pairs, each pair having one pole behind the other, and the pairs being separated by a set distance along the bank. Timing starts when the first two markers line up, and ends when the second pair line up. 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 133.3m per minute, and so the markers are set 133.3m apart.

On the River Thames, there are markers on the reaches above Teddington Lock

Teddington Lock

Teddington Lock is a complex of three locks and a weir on the River Thames in England at Ham in the western suburbs of London. The lock is on the southern Surrey side of the river....

, Sunbury Lock

Sunbury Lock

Sunbury Lock is a lock on the River Thames in England near Walton-on-Thames in north-west Surrey. The lock adjoins the southern bank about half a mile downstream of the Weir Hotel....

, Cookham Lock

Cookham Lock

Cookham Lock is a lock with weirs situated on the River Thames near Cookham, Berkshire. The lock is set in a lock cut which is one of four streams here and it is surrounded by woods. On one side is Sashes Island and on the other is Mill Island connected to Formosa Island, the largest on the...

, Sonning Lock

Sonning Lock

Sonning Lock is a lock and associated weir situated on the River Thames at the village of Sonning near Reading, Berkshire, England. The first lock was built by the Thames Navigation Commission in 1773 and it has been rebuilt three times since then....

, Day's Lock

Day's Lock

Day's Lock is a lock on the River Thames near Dorchester-on-Thames, Oxfordshire, England on the Dorchester side of the river.The pound lock was built in 1789 by the Thames Navigation Commissioner...

 and Osney Lock

Osney Lock

Osney Lock is a lock on the River Thames in Oxfordshire, England. It is close to Oxford where the village or island of Osney is next to the river.The first lock was built of stone by Daniel Harris for the Thames Navigation Commission in 1790....

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