Even on land, cargo can experience very substantial decelerations, particularly where containers are carried by rail. Although containers are now more often carried on dedicated point-to-point container trains, on long-distance movements marshalling cannot be eliminated altogether. Indeed practice in this respect differs from country to country and from operator to operator. Experts assess that deceleration forces of up to 4G can occur during traditional "hump-shunting" (where wagons are pushed to the top of a small hill and are then allowed to roll down the slope on to one of a number of different tracks to form new trains). Your editor recalls watching a demonstration of this technique a number of years ago, where huge baulks of timber proved totally inadequate to secure a load of steel tube in a shunt at about 20 kph (12 mph). In a container, unless cargo is tightly secured, it will shift under such shocks, creating bigger gaps and leading to more and more damage being done as the journey progresses. When carried by rail, containers may well travel "backwards" (ie with the doors at the front) so it is equally important to dunnage or secure cargo against shocks in either direction

Few shippers realise that their containers may be carried by rail. Because the container arrives at their premises on a road vehicle, they may well believe that they only need to pack it as they usually load a lorry itself for some domestic haulage. The essence of containerisation is, of course, that the unit can be carried multi-modally: the carrier may well decide that rail is the best way of moving the container for part of the overland journey. You and your clients should always pack containers for the worst eventuality.