Schedules allow for 12 freight trains to run each way through the tunnel every day when it opens but this allocation is already looking on the conservative side. All available space has been occupied and plans are afoot to treble the number of trains to 35 a day within a couple of years.
Optimists say that by the turn of the Century the Channel tunnel may have insufficient capacity for the 15 million tons of freight that could pass through it.
This is eight times the tonnage carried by the present service, which relies on special ferries to carry rail wagons across the Channel. It is also more than twice British Rail's immediate objective of 6 million tons.
Promoters of rail freight are concentrating on high-value traffic, such as motor parts, to maximise revenue.
Plans are being formulated to provide a service from the tunnel to Holyhead, and thence to Ireland, that would allow the carriage of lorries mounted on specially built, low-loading wagons. This would involve expenditure of up to pounds 100m on enlarging tunnels and raising bridges along the route from the Channel tunnel, but would be a big step in removing lorry traffic from British roads.
It is expected that the planners will seek assistance from Brussels since the improvements would have a dramatic effect on transport links between Ireland and the Continent. In particular, it would greatly help the railways to serve factories without direct rail links, since the lorries would simply drive off the train.
At the moment, such 'intermodal' links are constrained by the severe limits on the height and width of freight loads by much of Britain's Victorian railway system.
To compete with road transport, BR and its continental partners are having to promise extremely quick guaranteed journey times - 28 hours from London to Milan, for example. Without such guarantees it would be impossible to sell to retail chains needing to transport perishable food, and to motor manufacturers, now operating a just- in-time production chain.
Rail freight is also having to compete on price - a concept that is totally new to the historic railways practice of quoting a standard rate which is based on the length of the journey.
Many contracts cannot be signed until Eurotunnel gives British Rail an exact starting date. Originally scheduled for 14 March, this has now been postponed for a few weeks. Never the less, two large contracts for daily trainloads have already been signed by BR's Railfreight subsidiary.
The first is a three-year contract to carry Rover cars to Italy. The second contract, which is to start in August, is with the Spanish carrier Transfesa to transport automotive components from Ford's factory in Valencia to Dagenham.
This promising prospect contrasts with the uncertainties surrounding the other two services that will run through the tunnel. Le Shuttle, the service taking cars and lorries under the Channel in specially built wagons, will face tough competition from the ferry operators.
The direct passenger services from London to Paris and Brussels will undoubtedly be popular and profitable. Never the less, doubts remain over the capacity of BR's tracks to cope with the additional traffic during evening peak hours. In the early evening, travelling times could be up to 25 minutes slower than the normal three-hour journey from the new terminal at Waterloo to the Gare du Nord. This is because the international trains will be running between commuter trains, many of them made up of increasingly unreliable 30-year- old rolling stock.
The original plans for tunnel freight traffic meant that all the freight was to travel via a marshalling yard at Willesden in north-west London. But once this policy was abandoned, the way was opened to develop a network of freight terminals throughout Britain. By now, half a dozen are either open or in development in the Midlands, in northern England and in Glasgow (the latest development, at Wakefield in West Yorkshire, was announced last week). The French have also developed special terminals at such key points as Avignon and Perpignan near the Spanish frontier, which will be served by regular daily trains carrying a mixture of freight containers.
The only cloud is the late delivery of the special Type 92 locomotives developed by Brush to run over three different types of electrified track in France and Britain.
As a consequence, freight will initially have to be hauled by French locomotives through the tunnel to Dollonds Moor in Kent before being transferred to diesel locomotives for the onward journey to their final destination in Britain. However, the first Brush locomotives are now being tested, and the whole fleet should be in action before the end of the year.