Rule 10 — Traffic Separation Schemes
TL;DR — A vessel using a traffic separation scheme must proceed in the correct lane, join or leave at the termination or at a small angle, and cross lanes at as nearly right angles as practicable. Rule 10 applies in any condition of visibility and does not relieve any vessel of obligations under any other Rule. 33 CFR §83.10 33 CFR §83.04
---
What the Rule Says
Scope and Applicability
Rule 10 applies to traffic separation schemes wherever they exist. Critically, it does not stand alone: compliance with Rule 10 never relieves a vessel of her obligations under any other Rule in subchapter E. 33 CFR §83.10(a) Traffic separation schemes may be established for the purpose of these Rules, and vessel traffic service regulations may also be in effect in certain areas. 33 CFR §83.01(d)
Rule 10 falls within Rules 4 through 10, which apply in any condition of visibility — fog, rain, clear weather, day or night, it makes no difference. 33 CFR §83.04 This is a frequently tested point. Do not confuse Rule 10 with the "vessels in sight of one another" rules (Rules 11–18), which have a different applicability trigger. 33 CFR §83.11
---
Obligations of a Vessel Using a Traffic Separation Scheme
A vessel using a traffic separation scheme must do three things 33 CFR §83.10(b):
1. Proceed in the appropriate traffic lane in the general direction of traffic flow for that lane. 2. So far as practicable, keep clear of a traffic separation line or separation zone. 3. Normally join or leave a traffic lane at the termination of the lane. When joining or leaving from either side, do so at as small an angle to the general direction of traffic flow as practicable.
These three requirements work together. The intent is to keep vessels moving predictably in one direction, minimizing crossing and merging conflicts.
---
Crossing Traffic Lanes
A vessel shall, so far as practicable, avoid crossing traffic lanes. If crossing is obligatory, the vessel shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow. 33 CFR §83.10(c)
Note the word "heading" — the Rule specifies a heading at right angles, not necessarily a track made good at right angles. Current and leeway may affect the actual track, but the heading is what the Rule addresses.
---
Inshore Traffic Zones
A vessel shall not use an inshore traffic zone when she can safely use the appropriate traffic lane within the adjacent traffic separation scheme. 33 CFR §83.10(d)(i)
Exceptions — vessels that MAY use the inshore traffic zone regardless:
- Vessels of less than 20 meters in length
- Sailing vessels
- Vessels engaged in fishing
Additionally, any vessel — regardless of size or type — may use an inshore traffic zone when: 33 CFR §83.10(d)(ii)
- 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.
---
Separation Zones and Separation Lines
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: 33 CFR §83.10(e)
1. In cases of emergency to avoid immediate danger. 2. To engage in fishing within a separation zone.
The separation zone is the buffer between opposing traffic lanes. Keeping it clear is fundamental to the scheme's purpose.
---
Termination Areas
A vessel navigating in areas near the terminations of traffic separation schemes shall do so with particular caution. 33 CFR §83.10(f) Termination areas are where traffic from opposing lanes converges or disperses — a high-risk zone that demands heightened watchkeeping.
---
Anchoring
A vessel shall, so far as practicable, avoid anchoring in a traffic separation scheme or in areas near its terminations. 33 CFR §83.10(g) This is a "so far as practicable" standard, not an absolute prohibition, but anchoring within a scheme is strongly disfavored.
---
Vessels Not Using the Scheme
A vessel not using a traffic separation scheme shall avoid it by as wide a margin as is practicable. 33 CFR §83.10(h) This applies to vessels transiting nearby waters who have no need to enter the scheme.
---
Obligations of Fishing Vessels and Small Vessels Within the Scheme
Two separate paragraphs address the "shall not impede" standard: 33 CFR §83.10(i) 33 CFR §83.10(j)
- A vessel engaged in fishing shall not impede the passage of any vessel following a traffic lane.
- 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.
These are distinct obligations. A fishing vessel has a "shall not impede" duty regardless of its length. A sailing vessel has the same duty regardless of whether it is also engaged in fishing. These obligations coexist with the privilege those same vessel categories have to use inshore traffic zones.
---
Exemptions for Vessels Restricted in Ability to Maneuver
Two categories of vessels restricted in their ability to maneuver are exempted from Rule 10 compliance to the extent necessary to carry out their operations: 33 CFR §83.10(k) 33 CFR §83.10(l)
1. A vessel engaged in an operation for the maintenance of safety of navigation in a traffic separation scheme. 2. A vessel engaged in an operation for the laying, servicing, or picking up of a submarine cable within a traffic separation scheme.
---
Why It Matters on the Exam
OUPV and Master 100 GT written exams test Rule 10 heavily because it contains multiple specific numerical thresholds and categorical distinctions that lend themselves to multiple-choice questions. Key tested points include:
Visibility applicability. Rule 10 applies in any condition of visibility. 33 CFR §83.04 Exam distractors will suggest Rule 10 only applies when vessels are in sight of one another — that is incorrect. "In sight of one another" is the trigger for Rules 11–18. 33 CFR §83.11
Crossing angle. The Rule requires crossing on a heading as nearly as practicable at right angles — not at 45 degrees, not at the smallest angle. 33 CFR §83.10(c)
The 20-meter threshold. Vessels under 20 meters, sailing vessels, and fishing vessels may use the inshore traffic zone. However, those same vessels must not impede power-driven vessels following a traffic lane. 33 CFR §83.10(d)(i) 33 CFR §83.10(j)
Rule 10 does not override other Rules. Compliance with Rule 10 does not relieve any vessel of obligations under any other Rule. 33 CFR §83.10(a) A vessel in a TSS still must maintain a proper lookout, proceed at a safe speed, and take action to avoid collision under the applicable steering and sailing rules.
Fishing in a separation zone. Fishing within a separation zone is one of only two exceptions permitting a non-crossing, non-joining vessel to enter the separation zone. 33 CFR §83.10(e) However, that same fishing vessel must not impede vessels following a traffic lane. 33 CFR §83.10(i)
---
Common Pitfalls
Pitfall 1: Confusing "heading" with "track." The Rule says cross on a heading as nearly as practicable at right angles. 33 CFR §83.10(c) Candidates sometimes answer "course made good" or "track." The Rule specifies heading.
Pitfall 2: Assuming Rule 10 only applies in clear visibility. Rules 4 through 10 apply in any condition of visibility. 33 CFR §83.04 Rule 10 is not suspended in restricted visibility.
Pitfall 3: Thinking small vessels and sailing vessels are completely exempt from Rule 10 obligations. Vessels under 20 meters and sailing vessels may use the inshore traffic zone, but they still must not impede power-driven vessels following a traffic lane. 33 CFR §83.10(j) The privilege and the duty coexist.
Pitfall 4: Treating the "shall not impede" standard for fishing vessels and for small/sailing vessels as identical. The fishing vessel prohibition (paragraph (i)) applies to impeding any vessel following a traffic lane. 33 CFR §83.10(i) The small vessel/sailing vessel prohibition (paragraph (j)) applies specifically to impeding a power-driven vessel following a traffic lane. 33 CFR §83.10(j) These are not the same language.
Pitfall 5: Forgetting that Rule 10 does not relieve other obligations. A candidate may reason that because a vessel is complying with Rule 10, it has no further duties. Rule 10(a) expressly rejects this. 33 CFR §83.10(a)
Pitfall 6: Assuming anchoring in a TSS is absolutely prohibited. The Rule says "so far as practicable avoid anchoring." 33 CFR §83.10(g) It is a practicability standard, not an absolute prohibition. Exam questions may present it as a flat ban — that is incorrect.
---
Quick Check
Q1: In what conditions of visibility does Rule 10 apply?
Rule 10 applies in any condition of visibility. Rules 4 through 10 are not limited to vessels in sight of one another. 33 CFR §83.04
Q2: A vessel is obliged to cross a traffic lane. On what heading must she cross?
She must cross on a heading as nearly as practicable at right angles to the general direction of traffic flow. 33 CFR §83.10(c)
Q3: Which vessels may use an inshore traffic zone even when they could safely use the adjacent traffic lane?
Vessels of less than 20 meters in length, sailing vessels, and vessels engaged in fishing may use the inshore traffic zone. Additionally, any vessel may use it when en route to or from a port, offshore installation or structure, pilot station, or any other place within the inshore traffic zone, or to avoid immediate danger. 33 CFR §83.10(d)(i) 33 CFR §83.10(d)(ii)
Q4: A fishing vessel is operating within a separation zone. Is this permitted, and what obligation does she still carry?
Yes — fishing within a separation zone is one of the two exceptions that permit a vessel to enter a separation zone when not crossing or joining/leaving a lane. 33 CFR §83.10(e)(ii) However, the fishing vessel shall not impede the passage of any vessel following a traffic lane. 33 CFR §83.10(i)
Q5: Does full compliance with Rule 10 relieve a vessel of her obligations under the other steering and sailing rules?
No. Rule 10 expressly states it does not relieve any vessel of her obligation under any other Rule in subchapter E. 33 CFR §83.10(a)
Q6: A vessel restricted in her ability to maneuver is laying a submarine cable within a traffic separation scheme. Must she comply with Rule 10?
She is exempted from complying with Rule 10 to the extent necessary to carry out the cable-laying operation. 33 CFR §83.10(l)
Q7: A 15-meter sailing vessel is transiting a traffic separation scheme. A power-driven vessel is following a traffic lane. What obligation does the sailing vessel have?
The sailing vessel shall not impede the safe passage of a power-driven vessel following a traffic lane. 33 CFR §83.10(j) The sailing vessel's privilege to use the inshore traffic zone does not eliminate this duty.
Q8: Is anchoring within a traffic separation scheme absolutely prohibited?
No. A vessel shall so far as practicable avoid anchoring in a traffic separation scheme or in areas near its terminations. It is a practicability standard, not an absolute prohibition. 33 CFR §83.10(g)