Traffic Separation Schemes: Purpose and Limits of Maritime Traffic Lanes

A traffic separation scheme (TSS) organizes ship traffic into designated lanes. Opposing traffic flows are separated into traffic lanes, with a separation zone or separation line between them. These routing measures are intended to improve navigational safety, particularly in areas with crossing traffic or high traffic density.

Why traffic lanes are established

A TSS is a specific type of shipping route, not simply an arbitrary line drawn on a chart. The designated lanes organize opposing traffic flows. Other routing measures may also apply, such as recommended routes, precautionary areas or deep-water routes. These terms describe different elements of a broader system for organizing maritime traffic; not every recommended line is itself a traffic separation scheme.

Routing measures can also contribute to safety in areas where freedom of movement is limited. A TSS may therefore help make traffic movements more predictable.

Chart depiction and rules

The location and boundaries of a traffic separation scheme are shown on nautical charts and in the relevant official publications. For TSSs adopted by the International Maritime Organization (IMO), Rule 10 of the Collision Regulations governs the conduct of vessels within or near such schemes. This includes a specific requirement for crossing traffic lanes: vessels should cross the lanes, as far as practicable, at right angles to the general direction of traffic flow. The rule concerns traffic management within a TSS, not a blanket course instruction for areas outside it.

The wording “as far as practicable” is part of the requirement. The angle is measured relative to the general direction of traffic flow in the lane, not to a fixed compass direction or the orientation of the chart on screen.

A chart shows the spatial layout; Rule 10 sets out conduct requirements. They answer different questions. The difference between AIS, radar and nautical charts explains how the different information sources fit in. Other applicable rules and local requirements may also remain relevant to safe passage; the TSS does not replace them.

Traffic organization and the Collision Regulations

The other Collision Regulations also apply within a traffic separation scheme. Official nautical information describes the specific traffic situation in the area. A Vessel Traffic Service is a separate, shore-based traffic support service. The terms waterway, channel and navigational area describe different spatial contexts; the German inland navigation terminology explained there should not be equated with a maritime TSS.