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Conclusion

In general, underground space has the potential to break down the barriers resulting from increasing dispersion of the contemporary city in space and (travelling) time. However, an important distinction must be made between passive and active use of underground space in this respect.

Passively, underground space is put forward as an alternative after aboveground solutions seem to reach the limits of social and environmental acceptance. Most of these `symptom control' situations appear during the planning of large-scale infrastructure through open spaces and green areas. However, if actively used, the field of applications widens when underground space is employed to make cities more compact and dense while maintaining spatial and living qualities.

To make active use a feasible option, strategic application areas for underground space should be defined where multiplying effects, like eliminating environmental nuisances, improving accessibility and preserving spatial quality compensate for some of the more important limitations of underground space (daylight entry, building costs etc.).

Recent projects in the Randstad and Berlin are showing impressive and voluminous examples involving the use of underground space. However, it is not always easy to find a clear objective aimed at wider and more long-term goals, nor is a constant awareness apparent of the special architectural and urban design aspects essential for the acceptance of underground space by society.

The importance of the relationship between urban strategies, spatial and design qualities, and investments in underground building should be stressed here.

Although long-term planning without the use of underground space lacks dimension, underground building without clear long-term objectives amounts to digging blind like a mole.