Traffic Separation & Narrow Channels
Rules 9 and 10 of the COLREGs — how to navigate traffic separation schemes (TSS), narrow channels, and fairways safely.
Traffic Separation Scheme (TSS) — Layout
A TSS separates opposing traffic flows. Each lane carries traffic in one direction only, separated by a zone. Cross at right angles — never cut across at a shallow angle.
Traffic Separation Schemes
Rule 10Cross at right angles
A vessel crossing a traffic separation scheme must do so at as close to a right angle (90°) to the traffic flow as possible. This minimizes your time in the lane and presents a clear aspect to other traffic.
Rule 10(b)Do not join or leave at shallow angles
When joining or leaving a traffic lane, do so at the termination of the lane, or at as small an angle to the traffic flow as practical. Do not cut across at shallow angles.
Rule 10(b)Use inshore traffic zones correctly
Inshore traffic zones (between the lane and the coast) should not normally be used by through traffic. Local traffic, vessels <20m, sailing vessels, and fishing vessels may use them.
Rule 10(d)Avoid crossing the separation zone
Cross the separation zone (the gap between the two traffic lanes) at right angles, and as quickly as safe navigation allows.
Rule 10(b)Vessels <20m and sailing vessels
Small vessels and sailing vessels must not impede the safe passage of power-driven vessels following the traffic lane. They may use inshore traffic zones instead.
Rule 10(j)Fishing vessels must not impede
Fishing vessels shall not impede the passage of any vessel following a traffic lane. They must not fish in the separation zone or near lane terminations.
Rule 10(i)Narrow Channel — Keep to Starboard
In a narrow channel or fairway, keep to the starboard (right) side. Oncoming vessels do the same, passing port-to-port. Cross at right angles only.
Narrow Channels & Fairways
Rule 9Keep to starboard
A vessel proceeding along a narrow channel or fairway must keep as near to the outer limit of the channel on her starboard side as is safe and practicable.
Rule 9(a)Small vessels must not impede
A vessel of less than 20m in length, or a sailing vessel, must not impede the passage of a vessel that can safely navigate only within the channel.
Rule 9(b)Fishing vessels must not impede
A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway.
Rule 9(b)Crossing the channel
A vessel crossing a channel or fairway must do so at as close to right angles as possible. Do not cut across at a shallow angle — you spend more time in the channel and present a confusing aspect.
Rule 9(d)Overtaking
Overtaking is permitted, but the overtaking vessel must keep clear. In a narrow channel, the overtaken vessel may sound the danger signal (5+ short blasts) if the overtake is unsafe.
Rule 9(f)Do not anchor in a channel
If your vessel is likely to need to anchor, avoid doing so in a narrow channel or fairway. Anchoring in a channel blocks traffic and is prohibited.
Rule 9(g)"Do Not Impede" — A Key Obligation
Both Rules 9 and 10 use the phrase "shall not impede" — this is a specific legal obligation. It applies to small vessels (<20m), sailing vessels, and fishing vessels when near large vessels constrained by draft or following a traffic lane. "Do not impede" means you must not take any action that would require the other vessel to alter course or speed to avoid collision. If a risk of collision develops despite this, the normal give-way rules (Rules 12–18) then apply in addition.
Guidelines Only — Operator Responsibility. This is a general reference for COLREG Rules 9 and 10. TSS layouts, inshore traffic zone rules, and local channel regulations vary by location. Always consult current charts, Notices to Mariners, and local port authority guidance before navigating in or near a TSS or narrow channel. The operator is solely responsible for safety of the vessel and crew.