A Traffic Separation Scheme or TSS is a traffic-management route-system ruled by the International Maritime Organization

International Maritime Organization

The International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...

 or IMO.
The traffic-lanes (or clearways) indicate the general direction of the ships in that zone; ships navigating within a TSS all sail in the same direction or they cross the lane in an angle as close to 90 degrees as possible.

TSS's are used to regulate the traffic at busy, confined waterways or around capes. Within a TSS you normally see at least one traffic-lane in each main-direction, turning-points, deep-water lanes and separation zones between the main traffic lanes.
In most cases you can find an "inshore traffic zone" between the traffic-lanes and the coast.

A ship navigating in a traffic-lane should sail in the general direction of that lane. The body of water between two opposite lanes are no-go areas: shipping is not allowed in these areas (compare this with the central reservation

Central reservation

On divided roads, such as divided highways or freeways/motorways, the central reservation , median, parkway , median strip or central nature strip is the area which separates opposing lanes of traffic...

 of a road), so the risks for head-on collisions is greatly reduced.

The TSS rules are incorporated in the International Regulations for Preventing Collisions at Sea

International Regulations for Preventing Collisions at Sea

The International Regulations for Preventing Collisions at Sea 1972 are published by the International Maritime Organization , and set out, inter alia, the "rules of the road" or navigation rules to be followed by ships and other vessels at sea in order to prevent collisions between two or more...

 (under rule 10)

As said, when sailing within a lane of a TTS that ship has to follow the general direction of the lane. Where needed there are special zones where a lane splits into two channels: one ongoing and the other to the nearby port(s).

In most TTS schemes you will find Inshore Traffic Zones between the traffic-lanes and the coast. The inshore traffic zone is unregulated and shouldn't be used for ongoing traffic. It is meant for local traffic, fishing and small craft.

Well-known TTS locations include: The English Channel

English Channel

The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...

, German Bight

German Bight

German Bight is the southeastern bight of the North Sea bounded by the Netherlands and Germany to the south, and Denmark and Germany to the east . To the north and west it is limited by the Dogger Bank. The Bight contains the Frisian and Danish Islands. The Wadden Sea is approximately ten to...

, Singapore

Singapore

Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...

, and Cape Horn

Cape Horn

Cape Horn is the southernmost headland of the Tierra del Fuego archipelago of southern Chile, and is located on the small Hornos Island...

.

Crossing a TSS

If a ship wants to cross a traffic-lane it should do so at a right angle to avoid endangering ship traffic using the traffic-lanes (although traffic in the lane does not automatically have the right-of-way). To minimize the amount of time a crossing ship spend crossing the traffic-lanes, there should be a right angle between the lane direction and the keel direction - even if currents might shift the actual direction of the ship's movement to some angle other than 90 degrees.