What is the optimum tube diameter? A difficult answer to a very simple question!

Johan Visser, Research Institute Otb, Netherlands

Jan Katgerman, RUPS Adviseurs, Netherlands

Although feasibility studies show that underground freight transport project can be economic viable, the real and apparent barriers to implementing new systems are difficult to overcome. These barriers correlate very strongly to the financial risks and thus the financial feasibility of underground freight transport. In this paper, we focus on the optimal tube diameter to start with from a feasibility point of view? Therefore, we start to define the parameters, which are dominant in financial feasibility studies. The following parameters are critical:

· Exogenous parameters, such as cost of capital. The cost of capital is determined by the capital market.

· Market-related parameters, such as revenues. Revenues are strongly related to the segment of the market in which the system is introduced.

· System-related parameters, such as investment costs and expenditures. Both are strongly related to the type of system.

The challenge is now to define the optimal combination of market segment and transport system under the right exogenous conditions.

We will not deal with exogenous conditions. Contrasting the parameters of the transport system with those of the markets can be an illuminating exercise. On the one hand, we see a goal of minimizing investment costs; on the other, a goal maximizing revenues. If we want to minimise the investment costs, then:

· The tube diameter should be as small as possible but can have a longer trajectory length.

· The trajectory length should as short as possible but the tube diameter can be larger.

This limits the possible application areas to large diameter systems at short distances or small diameter systems at longer distances, thus avoiding high investment costs and long construction periods

If we want to maximise revenues, the following extremes are possible:

· High-volume deliveries, such as bulk transport. Despite the low prices, high revenues can be obtained through large volumes.

· High value deliveries in small quantities, such as parcels. High prices can lead to high revenues, even with small volumes.

High-volume deliveries can be profitable as long as the transport distances are small. But because of the high investment costs, long distances lead to a low profitability.

Small-volume deliveries, such as parcel deliveries can be profitable because of the low investment costs and the high prices. On the other hand, these systems can have problems maintaining a steady utilisation of the system.

Capsule pipeline systems are generally smaller than 1.3 metres, have the shape of a capsule and have no specific guidance systems, like a rail or pavement. Other underground transport systems make use of larger pipelines or tunnels, have a different shape from the capsules, and have some sort of guidance system. Capsule pipeline systems have a small pipeline diameter. Their field of application can be found in the transportation of homogenous goods, frequently only one type of good, at relatively low speeds and over short distance. On the other hand, the larger diameter systems are proposed for transportation of heterogeneous goods at higher speeds and longer distances.

The following applications can be suggested:

1. In urban areas, for the purpose of provisioning post offices, retail trade, catering establishments, office, and consumers.

2. Inside or between industrial complexes, logistical centres, and multi-modal terminals, such as airport and harbour complexes.

3. Collection or long distance transport of agricultural products, ore and solid waste.

4. Hinterland or cross-country transportation of maritime containers.

In almost all cases, feasibility studies showed that the projects were economically viable with or without some financial support from the government. All projects require a high investment in infrastructure. Project information shows that the proposed trajectory length has a considerable influence on the investment costs. In particular, the projects in application areas one and four show large trajectory lengths. In particular, the projects in application area four combine this with a large tube diameter, a doubly costly combination. From an economic feasibility point of view, application areas two and three are promising but require further investigation.

While it makes some sense to develop standards, it would be difficult to develop a single standard for all the different underground freight transport systems and different application areas; rather a set of standards for each type of application may be more appropriate. Finally, it will be worthwhile, when there is some consensus on the type of transport technology to be used, to consider standards for the tunnel or pipeline infrastructure.