Traffic Separation Scheme

A Traffic Separation Scheme (TSS) is an IMO-adopted routing measure that establishes designated traffic lanes in which vessels proceed in one direction only, separated by a defined separation zone or line, to reduce the risk of head-on collision in congested or geographically constrained waters. COLREG Rule 10 prescribes the obligations of vessels using traffic separation schemes, including joining or leaving only at the termination of the lane or at a shallow angle, keeping clear of the separation zone, and crossing only when necessary at a right angle to the general direction of traffic flow. TSSs are adopted by the IMO Maritime Safety Committee following submission by member states and are published in IMO chart publications and incorporated into official navigational charts. Well-known examples include the Dover Strait, the southern North Sea, the Strait of Malacca, and the waters around Ushant. Port state control officers and coastal state patrol vessels monitor compliance with TSS regulations, and violations — particularly crossing the scheme at an angle or navigating in the separation zone — are treated seriously. SOLAS V/10 requires masters to comply with IMO-adopted routeing measures.