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Rule 10
Traffic lanes are roads, not suggestions
Official rule text as published in the U.S. Coast Guard Navigation Rules
Source: USCG NavCen / eCFR Navigation Rules · Last updated September 7, 2026

(a) This Rule applies to traffic separation schemes [adopted by the Organization] and does not relieve any vessel of her obligation under any other rule.

(b) A vessel using a traffic separation scheme shall: (i) proceed in the appropriate traffic lane in the general direction of traffic flow for that lane; (ii) so far as is practicable keep clear of a traffic separation line or separation zone; (iii) normally join or leave a traffic lane at the termination of the lane, but when joining or leaving from either side shall do so at as small an angle to the general direction of traffic flow as practicable.

(c) A vessel shall, so far as practicable, avoid crossing traffic lanes but if obliged to do so shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow.

(d) (i) A vessel shall not use an inshore traffic zone when she can safely use the appropriate traffic lane within the adjacent traffic separation scheme. However, vessels of less than 20 meters in length, sailing vessels, and vessels engaged in fishing may use the inshore traffic zone. (ii) Notwithstanding Rule 10(d)(i), a vessel may use an inshore traffic zone when en route to or from a port, offshore installation or structure, pilot station, or any other place situated within the inshore traffic zone, or to avoid immediate danger.

(e) A vessel, other than a crossing vessel or a vessel joining or leaving a lane, shall not normally enter a separation zone or cross a separation line except: (i) in cases of emergency to avoid immediate danger; (ii) to engage in fishing within a separation zone.

(f) A vessel navigating in areas near the terminations of traffic separation schemes shall do so with particular caution.

(g) A vessel shall so far as practicable avoid anchoring in a traffic separation scheme or in areas near its terminations.

(h) A vessel not using a traffic separation scheme shall avoid it by as wide a margin as is practicable.

(i) A vessel engaged in fishing shall not impede the passage of any vessel following a traffic lane.

(j) A vessel of less than 20 meters in length or a sailing vessel shall not impede the safe passage of a power-driven vessel following a traffic lane.

(k) A vessel restricted in her ability to maneuver, when engaged in an operation for the maintenance of safety of navigation in a traffic separation scheme, is exempted from complying with this Rule to the extent necessary to carry out the operation.

(l) A vessel restricted in her ability to maneuver, when engaged in an operation for the laying, servicing, or picking up of a submarine cable within a traffic separation scheme, is exempted from complying with this Rule to the extent necessary to carry out the operation.

Color note: black text applies generally; blue is International Waters; green is Inland Waters.

MyCOLREGS explanation
Summary
Traffic separation schemes work like one-way lanes for vessel traffic: stay in your lane, go with the general flow, and stay clear of separation zones and lines when practicable. Join or leave a lane at a shallow angle when you can, and if you must cross a lane, cross it as close to a right angle as practicable. Avoid anchoring in or near a scheme, and if you're not using it, stay well clear of it. Small vessels under 20 meters, sailing vessels, and boats engaged in fishing can use the inshore zone, but none of them may block a power-driven vessel properly using the traffic lane. Vessels restricted in their ability to maneuver get a narrow exception when they're working on things like cable-laying or navigation safety within the scheme.
Real World Example
Traffic separation schemes exist in the world's most congested shipping choke points, where a loaded tanker running at 20 knots takes over a mile to stop - a small boat that treats the lane as merely advisory is gambling against physics, not just against a rule. Crossing at a right angle isn't about tidiness either - it's the heading that gets a small boat across the lane's high-speed traffic in the least possible time, minimizing the window where a much faster ship has to notice you and react.

Practice Questions

Q1. What must a vessel do when using a traffic lane within a traffic separation scheme?
A. Proceed in the appropriate lane in the general direction of traffic flow, and keep clear of separation lines/zones so far as practicable.
B. Anchor in the separation zone if it is convenient for a quick stop, since Rule 10 does not specifically prohibit anchoring there.
C. Choose whichever lane has less traffic, regardless of the general direction of flow.
D. Follow lane direction only if the vessel is a sailing vessel, since power-driven vessels are assumed to be more maneuverable and exempt.
Q2. A vessel must cross a traffic separation lane. What does Rule 10(c) require of her heading while crossing?
A. Crossing only when no other traffic is within 5 miles.
B. Matching the speed of surrounding traffic before crossing.
C. A heading as nearly as practicable at right angles to the general direction of traffic flow.
D. Following the lane briefly before cutting across at a shallow diagonal angle.

Practice Question Answers

Q1.
A. Proceed in the appropriate lane in the general direction of traffic flow, and keep clear of separation lines/zones so far as practicable. Rule 10(b) requires a vessel using a scheme to proceed in the proper lane with the general flow and, so far as practicable, keep clear of separation lines and zones. B describes something the scheme specifically prohibits. C substitutes traffic volume for the actual requirement, which is direction of flow. D limits the obligation to sailing vessels when it applies to everyone using the lane.
Q2.
C. A heading as nearly as practicable at right angles to the general direction of traffic flow. Rule 10(c) requires a vessel obliged to cross a traffic lane to do so on a heading as nearly as practicable at right angles to the flow, minimizing time spent in the lane. A and B each add a condition - clearance distance, speed matching - that Rule 10(c) doesn't require. D describes the diagonal, lingering crossing the right-angle rule exists specifically to prevent.