Navigation transit markers
Open-knowledge reference entry
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. 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 kilometres per hour (5.0 mph) or 133.3 m (437 ft) per minute, and so the markers are set 133.3 m apart.
On the River Thames, there are markers on the reaches above Teddington Lock, Sunbury Lock, Cookham Lock, Sonning Lock, Day's Lock and Osney Lock.
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This entry incorporates text from “Navigation transit markers” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.