A route of undefined width for the convenience of vessels in transit, indicated on charts but not mandatory.
In practice
Vessels are not legally compelled to follow a recommended track under SOLAS V/10 in the same direct way as a traffic separation scheme lane, but SOLAS V/34 requires masters to take all precautions dictated by the ordinary practice of seamen, and departure from a recommended track without good reason may be difficult to defend if an incident occurs. Officers of the watch must annotate their passage plan to indicate whether the vessel will follow the recommended track and must document any decision to deviate. ISM Code SMS requirements typically address the planning and execution of voyages through areas with adopted routeing measures.
Regulatory detail & full definition
A recommended track is an IMO-adopted routeing measure indicating a route across an area — typically open water with specific navigational hazards, fishing grounds, or environmental sensitivities — along which vessels are advised to proceed for safety or environmental reasons. Unlike a traffic separation scheme, the recommended track has no lane structure, no mandatory direction of travel, and no separation zone; it is a guidance measure only, published on official charts and in the IMO's 'Ships' Routeing' publication.
Vessels are not legally compelled to follow a recommended track under SOLAS V/10 in the same direct way as a traffic separation scheme lane, but SOLAS V/34 requires masters to take all precautions dictated by the ordinary practice of seamen, and departure from a recommended track without good reason may be difficult to defend if an incident occurs. Officers of the watch must annotate their passage plan to indicate whether the vessel will follow the recommended track and must document any decision to deviate. ISM Code SMS requirements typically address the planning and execution of voyages through areas with adopted routeing measures.