Even if the hunting and agricultural life 15 000–10 000 years ago used the sledge and the canoe, it was not until 3000 b.c. that land and water transport really advanced, through the horsedrawn carriage and the sailing boat. Roads, canals and harbours could now be used for passenger and freight transport. Cities effected a mobilisation of manpower and communication over long distances in space and time, because of the developments in agricultural productivity. In particular, miners, merchants, soldiers and priests were travelling widely. Cities were built in great river valleys: on the Indus and the Ganges rivers in India, on the Nile and the Euphrates and Tigris rivers in the west and on the Hwang Ho in the east. World trade between these districts began because India was rich in food and spices, but poor in metals. Transport made it possible to distribute surplus products and to obtain access to distant markets. Urban markets provided the means of procurement, storage, and distribution. Other dynamic elements were the wars and the pilgrimages which were early mass transport systems. Some important cities had a precinct sacred to the gods, with ancient burial pits and sacred shrines and memorials to which pilgrims made their journeys from distant places.1,2 Powerful cities extended their frontiers and destroyed people who might block their trade routes.
One of the constraints associated with transport is risk. A unit of measurement for risk is required for use in the analysis of transport capacity. As there is no escape from death, the issue that can be dealt with is how to make the current expected life span (approximately 600 000 hours) longer and less uncertain. Traffic density and safety are often inversely related. Safety, however, does not enter into capacity problems explicitly, but through different rules, equipment, design, etc.
It has become general practice to specify, by way of design standards, certain fixed values for the maximum traffic volume N at a route or terminal during a busy day or hour. These standards do not explicitly include the occupation time b of the route or terminal. One might therefore think of using the maximum traffic load Nb in a busy period. Such a standard would, however, be independent of the number of channels n (area) in use. The ratio of traffic load and the number of channels might then beused, the utilisation or service level Nb/n.1
The European Common Market Commission has estimated the percentage of the total working population in the E.E.C. engaged in transport at about 6 per cent, but this figure only includes carriers for hire or reward. When adjustments were made for private transport, and if subsidiary transport activities, such as railway construction and maintenance, were included, the figure was 16 per cent of the total working population.53
While the gross national products in the industrialised countries have increased by 4 per cent a year since the 1950s, industrial production by 6 per cent and world trade by 8 per cent, most traffic volumes have increased even more. Thus a very important point in intercity transport planning is the forecasting of future traffic volumes. In the following we shall first describe simple forecasting models, using the method of extrapolation.1
