COLREGS Rule 10 Traffic Separation Schemes with explanations

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Category: Seguridad marítima

Published on Sunday, 04 January 2026 08:06

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M.PUBLIC

Mandatory Procedures, Components, and Practical Guidance for Navigating TSS

WHAT IS A TRAFFIC SEPARATION SCHEME

Traffic Separation Schemes revolutionized navigation safety in congested waters by separating opposing traffic streams into distinct lanes. Think of them as maritime highways with one-way lanes divided by separation zones or lines. Vessels traveling opposite directions stay apart, dramatically reducing head-on collision risks. The system includes traffic lanes, separation zones, and inshore traffic zones working together to organize vessel movements through busy sea areas.

TSS Components and Structure

Every TSS consists of clearly defined elements serving specific purposes. Two one-way traffic lanes form the core, separated by either a separation line or a wider separation zone. The area between the TSS and the adjacent coastline becomes the inshore traffic zone, which operates under different rules. Additional routing measures like precautionary areas and areas to avoid often accompany TSS installations in particularly complex traffic situations.

Essential TSS Elements:
• Two one-way traffic lanes for opposing traffic streams
• Separation zone or line dividing the lanes
• Inshore traffic zone between TSS and coastline
• Traffic flow direction arrows marked on charts
• Entry and exit points at lane terminations
• Precautionary areas at junction points where applicable
• Clear outer limits defining lane boundaries

❕ Important: The inshore traffic zone is NOT part of the TSS itself. This distinction matters because Rule 10 only applies within the actual TSS boundaries, not in the ITZ.

TRAFFIC SEPARATION SCHEMES (RULE 10)

(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 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 subparagraph (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 manoeuvre 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 manoeuvre 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.

✔ Tip: IMO adopted TSS details appear in the "Ship's Routeing" publication. Annual updates and weekly changes publish in Admiralty Notices to Mariners, essential reading before transiting unfamiliar TSS.

WHEN TO USE A TSS

Deciding whether to use a TSS depends entirely on your intended passage. Vessels passing through congested areas where TSS exist should use them when safe to do so. The keyword here is necessity—if your route naturally takes you through the area the TSS serves, you're expected to use it. If your route bypasses the area, stay clear by as wide a margin as practicable to avoid interfering with vessels using the scheme.

Route planning determines TSS usage. A vessel heading through busy straits uses the appropriate TSS lane. A vessel passing nearby but heading elsewhere avoids the TSS entirely. The system works when everyone follows this logic—use it when you need it, avoid it when you don't.

TSS Usage Decision Factors:
► Confirm your route passes through the TSS operational area
► Verify adequate under-keel clearance throughout the lane
► Check for depth changes since last survey on your charts
► Consider meteorological and tidal effects on water depth
► Review any local regulations making TSS use mandatory
► Assess vessel size and cargo type for special requirements
► Plan entry point at lane terminations or appropriate angles

❔ Did you know? Local regulations sometimes make TSS use compulsory for all vessels or specific vessel types carrying certain cargoes. Check local requirements before assuming TSS use is voluntary.

Inshore Traffic Zone Usage

The ITZ serves specific purposes and vessel types. You can use it when proceeding to or from ports, offshore installations, pilot stations, or other locations within the zone. Local coastal traffic between ports within the ITZ operates there freely. Small vessels under 20 meters, sailing vessels, and fishing vessels may always use the ITZ. Otherwise, only enter the ITZ when necessary to avoid immediate danger, including seeking weather shelter.

ITZ Access Rights:
• Vessels less than 20 meters length
• Sailing vessels regardless of size
• Vessels engaged in fishing
• Local coastal traffic between ITZ ports
• Vessels accessing ports or installations within ITZ
• Vessels avoiding immediate danger
• Vessels seeking weather shelter

✘ Do not: Use the ITZ as a convenient shortcut when you should be using the TSS. The zone exists for specific purposes, not as an alternative route for through traffic avoiding TSS procedures.

PROCEEDING IN THE CORRECT LANE

Using the appropriate traffic lane sounds simple but errors occur with serious consequences. The appropriate lane carries traffic flowing in your direction. Proceeding in the wrong lane—against the traffic flow—creates immediate danger for every vessel in that lane. This fault alone makes you substantially liable for any collision that results. Vessels navigating correctly in their proper lane expect all traffic to flow in the same direction, not to meet opposing vessels head-on.

General Direction of Traffic Flow

You don't need to steer parallel to the lane sides or exactly match the traffic flow arrows on charts. You do need to maintain a course keeping you within the lane and away from its outer limits. This course will naturally form a small angle to the general traffic flow direction, allowing movement within the lane when needed—to overtake, for example, or to exit toward a port in the ITZ.

Lane Navigation Requirements:
► Proceed in the lane matching your direction of travel
► Maintain course generally aligned with traffic flow
► Keep as far as practicable toward starboard side of lane
► Stay clear of separation line or zone boundaries
► Avoid crossing into wrong lane unintentionally
► Keep course allowing safe lane navigation
► Leave sufficient room for other vessels in lane

❕ Important: While not required to keep to the extreme starboard edge like in narrow channels, you should keep toward the starboard side of the lane as far as practicable. This practice creates orderly traffic flow and leaves room for faster vessels to overtake.

Wrong Lane Navigation

Navigating in the wrong lane ranks among the most serious navigational faults. You create hazardous situations for yourself and every vessel properly using that lane. The danger exists in good visibility and multiplies dramatically in fog or restricted visibility. Even if other vessels see you and manage to avoid collision through their actions, you're still at fault for placing them in danger.

✘ Do not: Assume that because you can see other vessels and they can see you, proceeding in the wrong lane becomes acceptable. Visibility doesn't excuse wrong-lane navigation. The fault remains serious regardless of conditions.

JOINING AND LEAVING TRAFFIC LANES

Entering and exiting traffic lanes requires careful planning and execution. Normally, join or leave at the termination points where lanes begin or end. When this isn't practical and you must join or leave from the side, do so at as small an angle as practicable to the general traffic flow direction. This technique minimizes disruption to traffic already in the lane and clearly signals your intentions to other vessels.

Small angles to traffic flow mean you blend into the traffic stream smoothly rather than cutting across it sharply. Other vessels in the lane can easily assess your movements and understand you're entering or leaving rather than crossing. Sharp angles create confusion about your intentions and force other vessels to take avoiding action unnecessarily.

Entry and Exit Procedures:
• Preferably join or leave at lane termination points
• When joining from side, use small angle to traffic flow
• When leaving from side, use small angle to traffic flow
• Ensure your intentions clear to vessels in lane
• Avoid creating doubt about crossing versus joining intentions
• Monitor traffic already established in the lane
• Time your entry to avoid impeding lane traffic unnecessarily

✔ Tip: When joining from the side, start your turn early and make it gradual so your course change becomes obvious to other vessels. Sudden sharp turns create uncertainty about your intentions.

KEEPING CLEAR OF SEPARATION ZONES

Separation zones and lines exist to keep opposing traffic streams apart. Stay clear of them as far as practicable during normal operations. Don't use separation zones as convenient parking areas or shortcuts. They're safety buffers, not navigation areas. The only time you should enter a separation zone is during emergencies—engine breakdowns, for example, or when anchoring in bad visibility becomes necessary for safety.

Emergency anchoring in separation zones is acceptable seamanship when circumstances demand it. If mechanical failure leaves you unable to maintain position safely, anchoring in the separation zone removes you from active traffic lanes where other vessels navigate. Similarly, in dense fog when anchoring provides greater safety than attempting to navigate, the separation zone offers space away from traffic lanes.

Separation Zone Navigation:
► Keep clear of separation lines and zones during normal operations
► Avoid crossing separation zones except when necessary
► May anchor in separation zone during emergencies
► May anchor in separation zone during bad visibility for safety
► Use separation zone to avoid immediate danger when needed
► Never use separation zone as convenient parking or waiting area
► Exit separation zone as soon as emergency resolves

❕ Important: Anchoring in a TSS or near its terminations should be avoided under normal circumstances. Only emergency situations or bad visibility justify anchoring within TSS boundaries or separation zones.

CROSSING TRAFFIC LANES

Crossing traffic lanes requires careful judgment and precise execution. You should avoid crossing lanes whenever possible, but when obliged to cross, do so on a heading as nearly as practicable at right angles to the general traffic flow. This requirement minimizes your time in the lane and creates a clear crossing situation with vessels navigating in the lane. Right-angle crossings make your intentions obvious and allow other vessels to assess the situation properly.

When Crossing Becomes Necessary

You're only obliged to cross a traffic lane when necessary. Necessity means your voyage requires crossing—you're accessing a port, installation, or location beyond the lane, or you need to cross to join another lane for your onward passage. Crossing just because it's convenient isn't necessity. Traffic lanes should remain clear for vessels proceeding correctly along them except when others must cross them or enter them for legitimate navigational reasons.

Legitimate Crossing Situations:
• Proceeding to port or installation beyond the lane
• Joining opposite lane for onward passage
• Accessing pilot station across the lane
• Emergency requiring crossing to avoid danger
• Seeking shelter in ITZ or separation zone
• Avoiding immediate danger requiring lane crossing

The Right Angle Requirement

Crossing on a heading at right angles means your course through the water—not over the ground—must be perpendicular to the traffic flow direction. The 1987 amendments added "on a heading" specifically to clarify this point. Your heading matters, not your track over the ground. Current or wind affecting your track doesn't change your obligation to steer the right-angle heading.

Right Angle Crossing Technique:
► Determine general direction of traffic flow from chart
► Calculate heading at right angles to this flow direction
► Steer the calculated right-angle heading
► Maintain right-angle heading throughout crossing
► Ignore drift from current—heading matters, not track
► Don't alter toward parallel with lane traffic
► Complete crossing without unnecessary course changes

✘ Do not: Cross at shallow angles thinking you'll join the lane smoothly afterward. If you're crossing, cross at right angles. If you're joining, join at a small angle. Don't confuse the two maneuvers—they're different and require different techniques.

Safe Crossing Timing

Only cross when safe to do so. Safety means vessels in the lane have sufficient time to appraise the situation and take appropriate action if necessary. The crucial moment for judging safety is when you decide to cross, not when you actually enter the lane. Make your crossing decision when vessels in the lane are far enough away that your crossing won't create risk of collision requiring their immediate action.

What constitutes sufficient time depends on circumstances, but general guidance suggests vessels should have at least 12 minutes to take avoiding action if needed, with additional time for proper situation appraisal beforehand. When making your crossing decision, consider whether vessels in the lane five miles or more distant would be considered "far away" and whether your crossing at right angles would allow passing without risk.

Crossing Safety Assessment:
• Assess traffic in lane before committing to cross
• Ensure vessels in lane are sufficiently distant
• Five miles or more typically considered adequate separation
• Allow time for other vessels to appraise situation
• Allow time for avoiding action if necessary (minimum 12 minutes)
• Consider visibility conditions affecting appraisal time
• Don't cross in face of approaching traffic
• Wait for traffic to pass if separation inadequate

✔ Tip: If in doubt whether it's safe to cross, wait. You can always wait for traffic to pass and then cross safely. You can't undo a bad crossing decision once committed.

CROSSING MULTIPLE LANES

The right-angle crossing requirement applies whether you're crossing one lane or both lanes of a TSS. Some mariners incorrectly believe they can cross the first lane at less than right angles if they plan to join the second lane. This interpretation is wrong. You must cross each lane at right angles to its traffic flow. The obligation to join a lane at a small angle applies only after you've crossed the separation zone and are ready to enter the lane you're joining.

The technique for crossing both lanes involves crossing the first lane at right angles, maintaining that heading through the separation zone, then altering course in the separation zone to join the second lane at a small angle. Don't try to combine crossing and joining into one diagonal course across both lanes—this violates the right-angle crossing requirement and creates confusion for vessels in both lanes.

Two-Lane Crossing Procedure:
1. Calculate right-angle heading for first lane's traffic flow
2. Steer right-angle heading crossing first lane
3. Continue right-angle heading through separation zone
4. Alter course in separation zone before entering second lane
5. Enter second lane at small angle to its traffic flow
6. Blend into second lane traffic stream smoothly

❕ Important: The expression "as nearly as practicable" in the right-angle crossing requirement doesn't give you license to cross at convenient angles. It acknowledges practical limitations like avoiding immediate danger, but absent such limitations, cross at right angles.

PRECAUTIONARY AREAS

Precautionary areas appear at junction points where traffic from various directions meets and true traffic separation becomes impractical. In these complex junctions the lane-specific steering mandates of Rule 10(b) and 10(c) (for example, right-angle crossings and small-angle joining) do not apply in the same strict way as inside traffic lanes. However, Rule 10(f) — the obligation to navigate with particular caution when near TSS terminations — still applies, and the normal COLREGS (Rules 4–19) remain fully in force. In short: lane-specific prescriptions are relaxed, but caution and standard collision-avoidance rules continue to govern behaviour.

Navigating in Precautionary Areas

Though some lane-specific parts of Rule 10 are not applied in precautionary areas, that does not remove the duty of safe navigation. Vessels must still follow the COLREGS (Rules 4–19) for meeting, crossing and overtaking, and apply Rule 10(f)'s requirement to proceed with particular caution near TSS terminations. No vessel gains special privilege merely by following a through-going route; each encounter must be judged on its own facts using standard collision-avoidance practice.

Precautionary Area Navigation:
► Recognize precautionary area boundaries on your charts
► Increase vigilance when entering precautionary areas
► Expect vessels on various courses and headings
► Apply normal COLREGS rules for meeting situations
► Don't assume right of way based on lane direction
► Make intentions clear through course and speed
► Communicate with other vessels when appropriate
► Navigate with particular caution throughout the area

❔ Did you know? Precautionary areas often have recommended traffic flow directions shown on charts, but these are recommendations only, not mandatory like traffic lane directions in TSS.

Crossing in Precautionary Areas

If you intend to cross a traffic lane and a precautionary area exists where you plan to cross, consider using it. Traffic in lanes expects to meet crossing vessels in precautionary areas. While not obliged to cross there, doing so when practical makes sense. Even though Rule 10 doesn't apply in precautionary areas, good seamanship suggests crossing at right angles to traffic flow as you would elsewhere. This maintains predictability and clarity for all vessels.

Precautionary Area Crossing:
• Consider crossing lanes in precautionary area when available
• Traffic expects crossings in these areas
• Still cross at right angles as matter of seamanship
• Make intentions clear through course and actions
• Don't assume Rule 10 protections apply
• Normal crossing rules determine stand-on and give-way status
• Avoid precautionary areas unless using TSS or accessing nearby ports

✔ Tip: When crossing in a precautionary area, your right-angle crossing course still makes your intentions clearest to other vessels, even though not technically required by Rule 10 in that area.

APPROACHING AND ENTERING TSS

Vessels approaching TSS must navigate with particular caution near the terminations where lanes begin or end. This requirement applies whether you intend to use the TSS or avoid it. The area near terminations sees vessels entering, leaving, and passing by, creating complex traffic situations requiring heightened awareness. Good seamanship demands that you approach TSS entrances on a course following the general traffic flow direction for your intended lane.

Proper Entry Technique

Approach the entrance to your chosen traffic lane from a position well away from the termination, on a course aligned with the lane's traffic flow direction. This mirrors the principle for entering narrow channels—approach on the mid-channel course from a distance. As you draw closer to the entrance, move toward the starboard side of the lane. This technique makes your intentions clear, allows traffic already in the lane to assess your approach, and enables smooth integration into the traffic flow.

TSS Entry Procedures:
► Identify correct lane for your direction of travel
► Approach from position well before lane termination
► Align your course with lane's traffic flow direction
► Maintain this course as you approach entrance
► Move toward starboard side as you near entrance
► Enter lane without crossing traffic or creating obstruction
► Integrate smoothly into established traffic flow
► Avoid sudden course changes after entering

✘ Do not: Approach TSS entrances at angles divergent from the traffic flow, then make sharp turns to enter the lane. This creates confusion about your intentions and may cause other vessels to take unnecessary avoiding action.

Avoiding TSS

When your route doesn't require using a TSS, avoid it by as wide a margin as practicable. Don't pass close along its edges or cut across terminations unnecessarily. Give the entire TSS area wide berth so vessels using it have sea room for navigation and maneuvering. Particular caution near terminations applies equally to vessels avoiding the TSS—traffic entering and leaving creates complex situations requiring awareness from all vessels in the vicinity.

TSS Avoidance Procedures:
• Route to pass well clear of TSS boundaries
• Maintain wide margin when passing TSS
• Avoid passing through terminations unnecessarily
• Navigate with particular caution near terminations even when avoiding
• Don't cut corners across termination areas
• Give sea room to vessels entering or leaving TSS
• Monitor traffic in TSS even when not using it

❕ Important: Rule 10 applies not just to vessels in the TSS but also to vessels near the TSS. Your obligation to navigate with particular caution near terminations exists whether you're using the scheme or avoiding it.

FISHING VESSELS AND SMALL CRAFT

Vessels engaged in fishing must not impede passage of vessels following traffic lanes. This prohibition is absolute—fishing operations don't excuse blocking or hindering lane traffic. If fishing activities would impede lane traffic, don't fish there. Choose fishing grounds outside traffic lanes where your activities won't interfere with through traffic. The same prohibition applies to vessels under 20 meters length and sailing vessels—don't impede power-driven vessels following traffic lanes.

These vessel types may use the inshore traffic zone freely, providing logical alternative operating areas. Small craft, sailing vessels, and fishing vessels can conduct activities in the ITZ without interfering with TSS traffic. This arrangement balances the needs of various vessel types—large commercial traffic uses the TSS lanes efficiently while smaller vessels and fishing craft operate safely in designated alternative areas.

Small Vessel TSS Operations:
► Vessels engaged in fishing shall not impede lane traffic
► Vessels under 20 meters shall not impede lane traffic
► Sailing vessels shall not impede lane traffic
► All these vessels may freely use the ITZ
► Choose fishing grounds outside active traffic lanes
► Transit through lanes quickly without impeding traffic
► If using lanes, follow same rules as other vessels
► Don't assume right to impede larger vessels

✔ Tip: If you're fishing near a TSS, monitor VHF for traffic in the lanes and be prepared to move your gear if vessels need to maneuver to avoid you. Prevention beats the problems that follow impeding lane traffic.

TRAFFIC FLOW DIRECTION INTERPRETATION

Understanding general direction of traffic flow prevents confusion when navigating TSS. The general direction isn't necessarily the exact course shown by traffic arrows on charts, nor must it be precisely parallel to lane boundaries. It represents the overall direction traffic flows through the lane. Individual vessels within the lane may vary from this general direction by small amounts while still complying with the flow requirement.

This flexibility allows vessels to move within the lane as needed—shifting toward the starboard side, overtaking slower traffic, or positioning to exit the lane. The key is maintaining a course generally aligned with the flow direction, not exactly matching it. Your course should keep you in the lane moving in the correct general direction, not fighting against the traffic stream or creating angles that suggest you're crossing rather than following the lane.

Traffic Flow Compliance:
• Follow general direction shown by traffic arrows
• Small variations from exact arrow direction acceptable
• Maintain course keeping you in correct lane
• Don't interpret flexibility as license for large deviations
• Course should clearly indicate lane-following not crossing
• Other vessels should easily recognize you're in proper lane
• Avoid courses suggesting wrong-way or crossing intentions

❔ Did you know? The "as far as practicable" qualification appears in several Rule 10 requirements, acknowledging that perfect compliance isn't always possible. This doesn't excuse poor planning or seamanship—it recognizes genuine practical limitations only.

OVERTAKING IN TRAFFIC LANES

Overtaking within traffic lanes follows normal overtaking rules—the overtaking vessel keeps clear of the vessel being overtaken. What changes in TSS is the space available for overtaking. You must overtake within your lane, which may require the vessel being overtaken to facilitate the maneuver by keeping well to starboard. Both vessels share responsibility for safe overtaking—the overtaking vessel for keeping clear, and the vessel being overtaken for maintaining steady course and speed without impeding the overtake.

Plan overtaking maneuvers carefully within the confines of traffic lanes. Ensure sufficient sea room exists in the lane for the overtake without forcing you near the separation line or zone. If insufficient room exists, you may need to wait until the lane widens or the vessel ahead exits the lane. Never attempt overtaking by crossing into the opposite traffic lane—this creates the wrong-lane navigation fault with its serious consequences.

Overtaking Procedures in Lanes:
► Assess available sea room in lane before overtaking
► Ensure overtake can be completed within lane boundaries
► Vessel being overtaken should keep to starboard of lane
► Overtaking vessel keeps clear throughout maneuver
► Don't cross into opposite lane to overtake
► Don't impede opposite-direction traffic during overtake
► Complete overtake and return to starboard side of lane
► Abort overtake if conditions become unsafe

✘ Do not: Assume you can cross into the opposite traffic lane to overtake in a TSS. This isn't a two-way road where you can temporarily use the opposite lane. It's a one-way system where opposite lanes carry opposing traffic.

OTHER RULES STILL APPLY

Rule 10 explicitly states it doesn't relieve any vessel of obligations under other rules. All COLREGS rules remain in force within TSS. Steering and sailing rules for vessels in sight of one another (Rules 11-18) apply fully. Restricted visibility rules (Rule 19) apply when visibility decreases. Safe speed, lookout, risk of collision, and all other fundamental rules continue to govern your actions regardless of TSS navigation.

This means that properly navigating in a TSS doesn't automatically protect you from liability if you violate other rules. Maintaining proper lookout, proceeding at safe speed, and taking timely avoiding action when risk of collision exists remain your responsibilities. TSS rules supplement other rules, they don't replace them. Consider TSS navigation as an additional layer of regulation working alongside fundamental collision avoidance rules.

Continuing Rule Obligations:
• Rule 5 - Maintain proper lookout at all times
• Rule 6 - Proceed at safe speed for conditions
• Rule 7 - Determine if risk of collision exists
• Rule 8 - Take action to avoid collision
• Rules 11-18 - Follow steering and sailing rules in sight
• Rule 19 - Follow restricted visibility procedures
• All other rules remain fully applicable

✔ Tip: Think of Rule 10 as organizing traffic flow, while other rules govern individual vessel interactions within that organized flow. You need both—organized traffic patterns and proper collision avoidance within those patterns.

ANCHORING IN TSS

Vessels should not anchor in TSS or in areas near terminations except in emergencies. This prohibition exists because anchored vessels obstruct traffic lanes, creating hazards for vessels navigating at speed through the area. An anchored vessel in a traffic lane forces other vessels to maneuver around it, potentially pushing them toward the separation zone or opposite lane, creating dangerous situations.

Emergency situations justify anchoring in TSS. Engine breakdowns leaving you unable to control your vessel require anchoring to prevent drifting into more dangerous positions. Bad visibility sometimes makes anchoring safer than attempting to navigate, particularly when you can anchor in the separation zone rather than in active traffic lanes. These emergency anchorages should be as brief as possible, leaving the TSS as soon as circumstances permit.

Anchoring Guidelines:
► Avoid anchoring in TSS during normal operations
► Avoid anchoring near termination areas
► Emergency situations may justify anchoring
► Consider separation zone for emergency anchoring
► Bad visibility may justify anchoring for safety
► Make situation known to other vessels via VHF
► Display appropriate shapes and lights for anchored vessel
► Leave TSS as soon as emergency resolves
► Consider alternatives like drifting in separation zone temporarily

❕ Important: If you must anchor in a TSS due to emergency, broadcast your position and situation on VHF to warn approaching traffic. Display anchor signals properly and maintain radio watch continuously.

LOCAL REGULATIONS AND MANDATORY ROUTING

Some TSS operate under local regulations making their use mandatory for all vessels or specific vessel categories. These regulations may require certain vessel types or cargo carriers to use designated lanes, prohibit other vessel types from using the TSS, or impose additional requirements beyond Rule 10. Check local regulations before entering any TSS to understand whether mandatory routing applies and what additional requirements you must meet.

Even in non-mandatory TSS, following Rule 10 constitutes good seamanship. The routing measures exist to improve safety, and complying with them serves that safety purpose whether legally mandatory or not. Treating all TSS as if mandatory and complying with Rule 10 in all of them establishes consistent safe practices regardless of varying local requirements.

Regulatory Compliance:
• Check local regulations before using each TSS
• Determine if TSS use is mandatory for your vessel type
• Verify cargo-specific routing requirements
• Confirm any prohibited areas or restrictions
• Understand reporting requirements if any exist
• Follow Rule 10 even in non-mandatory TSS
• Consider TSS compliance as standard practice regardless of local law
• Monitor VHF for traffic information and regulations

✔ Tip: Admiralty Sailing Directions for each area contain local TSS regulations and requirements. Review these during voyage planning, not after entering the TSS.

VISIBILITY AND TSS NAVIGATION

TSS navigation in restricted visibility demands extra caution beyond normal restricted visibility procedures. Vessels proceeding in wrong lanes, crossing improperly, or navigating outside normal traffic patterns create magnified dangers when visibility drops. The assumptions other vessels make about traffic patterns in TSS—vessels in lanes proceeding in proper directions, crossing vessels at right angles—become critical for collision avoidance when visual verification becomes impossible.

Reduced visibility doesn't change your TSS navigation obligations under Rule 10. You still must proceed in the correct lane, cross at right angles, and follow all other TSS procedures. What changes is the reduced margin for error and the increased consequences of mistakes. Other vessels navigating in fog or restricted visibility rely heavily on the predictability TSS routing provides. Breaking those patterns creates unpredictable situations when vessels have limited ability to detect and react to your movements.

Restricted Visibility TSS Operations:
► Maintain all Rule 10 compliance in restricted visibility
► Reduce speed to safe speed for conditions
► Post extra lookouts as conditions require
► Use radar plotting to track traffic in lane
► Make proper sound signals as required
► Avoid crossing lanes unless absolutely necessary
► If must cross, cross at precise right angles
► Consider waiting for visibility to improve before crossing
► Proceed in correct lane maintaining predictable track
► Don't assume other vessels will detect wrong-lane navigation

❕ Important: Wrong-lane navigation becomes dramatically more dangerous in restricted visibility. Other vessels navigating correctly in their lanes don't expect to meet opposing traffic and have limited ability to detect and avoid you.

Good to Know

IMO General Provisions on Ships' Routeing provides detailed guidance beyond Rule 10, covering recommended practices and procedures for various routing measures including TSS.

Ship's Routeing publication by IMO lists all IMO-adopted TSS with detailed charts, descriptions, and specific requirements for each scheme.

Weekly Admiralty Notices to Mariners published by UKHO contain changes and updates to existing TSS, essential reading to maintain current knowledge of scheme modifications.

Two-way routes within some TSS exist where vessels should keep to the starboard side far as practicable, similar to narrow channel requirements but less strictly enforced.

Deep-water routes often appear within or adjacent to TSS, designated for deep-draft vessels requiring maximum available depth with different usage rules than standard traffic lanes.

Recommended routes differ from TSS lanes in being advisory rather than mandatory, though good seamanship suggests following them in the recommended direction.

Areas to be avoided often surround TSS where navigation is prohibited or strongly discouraged due to environmental sensitivity, hazards, or other factors.

Coastal state authority over TSS in territorial waters allows local regulations differing from international standards, making local regulation review essential.

Right-angle crossing requirement added in 1987 amendments clarified earlier ambiguous language about crossing "at right angles," explicitly requiring heading not track to be perpendicular.

Heading versus track distinction matters because current and wind create different tracks over ground than headings steered, but Rule 10 cares about heading only.

Stand-on vessel status remains valid for crossing vessels even if their crossing violated good seamanship by occurring at an unsafe time, though they bear fault for the unsafe crossing decision.

Precautionary areas at busy junctions sometimes contain sub-zones with different recommended directions, creating layered traffic organization within the cautionary area.

Roundabout systems appear in some TSS where multiple routes converge, requiring vessels to circulate in designated directions similar to road traffic roundabouts.

Designated anchorages adjacent to some TSS provide proper anchoring areas outside traffic lanes for vessels waiting for berths or other purposes.

Traffic clearance or reporting requirements apply in some TSS where vessels must report positions or obtain clearance before entering certain areas or lanes.

Speed limitations occasionally apply in TSS near environmentally sensitive areas or where whale strikes pose risks, supplementing general safe speed requirements.

Seasonal variations in some TSS shift lanes or modify boundaries based on ice conditions, weather patterns, or marine life migration routes.

One-way traffic only in TSS lanes means no provision exists for vessels to proceed opposite the designated direction regardless of circumstances except emergencies.

Chart symbols and notations for TSS include magenta boundaries, arrows showing traffic flow direction, and various symbols for precautionary areas and other routing measures.

Electronic chart display of TSS must be verified against paper charts during passage planning as electronic boundaries may not precisely match official descriptions.

Under-keel clearance planning for TSS must consider survey age, seabed changes, and tide/current effects on actual depths available versus charted depths.

Pilot boarding near TSS requires careful coordination to avoid creating obstruction in lanes while making lee or waiting for pilot craft.

Emergency tug availability in major TSS provides response capability for disabled vessels before they create hazards to lane traffic.

VTS operations in many major TSS monitor traffic, provide information, and sometimes issue instructions for traffic organization and collision avoidance.

AIS mandatory carriage requirements support TSS safety by making all vessels visible to each other and VTS authorities monitoring traffic flow.

Weather routing services must consider TSS compliance when calculating optimal routes, as diversions to avoid weather cannot violate TSS requirements without justification.

Passage planning notation for TSS transits should identify entry points, crossing locations if applicable, exit points, and contingency anchoring positions for emergencies.

Bridge team briefing before entering TSS should cover specific lane entry procedures, crossing plans if applicable, and emergency procedures relevant to the particular scheme.

• Rule 2 COLREGs: Responsibility with Explanations
• Rule 5 COLREGs: Look-out with Explanations
• Rule 6 COLREGs: Safe Speed with Explanations
• Rule 7 COLREGS: Risk of Collision with Explanations
• Rule 8 COLREGs: Action to Avoid Collision with Explanations
• Rule 9 COLREGS Narrow channels with Explanations
• Rule 10 COLREGs: Traffic Separation Schemes with Explanations
• Rule 13 COLREGs: Overtaking with Explanations
• Rule 14 COLREGs: Head-on Situation with Explanations
• Rule 19 COLREGs: Conduct of Vessels in Restricted Visibility

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