Vessels heading south west from the North Sea to the Atlantic are expected to sail on the English side of the Channel and those coming up from the Atlantic are told to sail closer to France. Such ships - there are around 300 of them every day - are meant to avoid the mid-Channel area.
However there are "cross-over points" where ships from Continental Channel ports can join those voyaging into the Atlantic by cutting across those heading north east. There are similar cross-over points for vessels which want to head for the North Sea, but come from the English side
To complicate matters further there are another 200 ships a day which simply cross from one side of the Channel to the other. In yesterday's incident the Ever Decent, a Taiwan-owned and Panama-registered container ship, collided with the US-owned and Bahama-flagged passenger liner Norwegian Dream at a recognised crossing point.
While the Straights of Dover are arguably the busiest waterway in the world they are incontestably the most tightly controlled. In the 1960s there were a whole series of accidents in the Channel and in 1967, it became the first waterway to have a routing system. The Channel became safer, but there were still a series of collisions and in 1977 the traffic separation system became mandatory. That has had a significant impact, although nine people were killed in 1993 when a BP oil tanker, British Trent, was rammed by a South Korean-crewed bulk carrier in tick fog off Ostend. At the inquest the coroner said the collision would not have happened if the bulk carrier, Western Winner, had observed fundamental rules.
Earlier, in 1991, a National Audit Office report warned that the Channel and the North Sea were at risk of an environmental disaster because of the huge increase in tanker traffic.
On 1 July this year, the rules governing shipping in the Channel were tightened further. A voluntary scheme whereby captains entering the area reported their name, position and intended route became compulsory, because less than 30 per cent of ships had co-operated with the informal system.
Leaders of the ships officers' union, Numast, believe that there is still considerable room for improvement. In discussions with the Department of the Environment, Transport and the Regions, Numast has urged ministers to introduce regulations which would put the Marine and Coastguard Agency's traffic service roughly on a par with air traffic control. Under such a regime "sea traffic controllers" would have the right to order ships to take certain routes.
But Peter McEwen, deputy general secretary of the union, said that with a growing shortage of skilled and experienced seafarers, better recruitment and training were needed.