18 Since 1985 they have been disaggregated and analyzed for both containerized and noncontainerized traffic. The analysis of the disaggregation of cargo looked into imports and exports figures for the country, transshipments and transit figures and origin/destination relations.

Forecast consists essentially of extrapolations provided by an econometric modeling of the historical traffic. The main explanatory variables for the future of traffic are taken to be: (i) the general business cycle and trends variable in Belgium (the evolution of the share of exports and imports in GDP and the evolution of industrial production) and a similar variable in a large range of trading partners (an index of GDP in the EEC, the USA and Japan), as well as international trends in containerization, the specific variable depends on the traffic to forecast; (ii) the competition (remember that there are many competing ports close by); (iii) the microeconomic features that make the port interesting for specific traffic (it is the second petrochemical port in the world for instance).

The 1996 Masterplan for the port shows how the quantitative part of the forecast was made for every major traffic groups. For general cargo, the variable used to pick up the business cycles and trends is an index of GDP in the developed world (EEC, USA and Japan). For bulk cargo, the driving force is assumed to be industrial production in the EEC. For both cases, the importance of competing ports in determining prospects is taken in the Hamburg-Le Havre range which covers all the major competing ports. It is summarized into Antwerp's market share in this corridor. The plan also presents a qualitative forecast. It covers an assessment of general cargo traffic disaggregated into specific commodity groups (iron and steel, non-ferro metals, fertilizers, wood products, vegetable and fruits, grains and animal fodders, rolling material, flowers, sugar, food and other. For bulk traffic, the experts are asked to consider ores, solid fuels, grains and animal fodder, fertilizers, sand, crude oil and chemical products (including petro-chemical).

Overtime the quantitative models' performance disappointed and it became increasingly used only to supplement a more qualitative approach. Indeed, the quantitative model was overestimating quite significantly (between 16.5% for general cargo and 37.3% for total seaborne cargo). The qualitative method generated an underestimate of 1.6% for 1985 when it was first used (with a deviation of +9.1 % to -14,6% for different targeted activities). This is why the qualitative approach is in fact used to generate information which is then built-in the more aggregate quantitative forecast of the demand for port services (in terrns of tons) .

But forecast modeling is an evolving science also in ports and the amazing growth in containerized traffic is generating interesting progress in the field as seen in the case of Antwerp as well. The initial step is to estimate how the overall macroeconomic prospects influence the overall general cargo traffic (defined as conventional cargo traffic + container traffic + roll-onroll-off traffic) in the competitive region (i.e. the Hamburg-Le Havre market segment). This is taken to follow a simple trend in which an increase in 1 point in an index of the world GDP results in an increase of 2.307 in general cargo traffic in the corridor (but this effect is reassessed every year using the latest information available on the linkages between the two variables). The future containerization rate is the next aspect forecasted. It is also an extrapolation but it recognizes that the degree of containerization is limited and the growth will eventually start to decrease. This drives the choice of the functional form to a semi-logarithmic function (i.e. the degree of containerization (Y) is explained by the logarithm of a time trend (T): Y=.61+.04 InT) but the specific parameters of this equation are picked by experts rather than simply estimated analytically from past data . Jointly with the first step, it yields an overall regional containerization forecast which is an average figure since the experts recognize that its evolution will vary for the various departure/destination combinations. This is then used to generate a traffic forecast for containers in the corridor. In 1996, it was expected to increase from 140.6 million tons in 1995 to 184.5 in 2000 and 227.5 in 2005.