The Copenhagen Harbour Tunnel Project

The initial stages of the planning process concerning large infrastructure projects are often based on rather simplified modelling efforts - if any. Based on this, large-scale traffic modelling studies are often agreed upon. However, even though traffic models are becoming more and more complex, a number of simplifications are often decided upon in the early stage of the study, e.g. whether to model induced traffic and land use interaction. Even if the best practice is followed, the forecasts may turn out far from the actual flows. In addition, the work is often so comprehen-sive, that only few alternatives are examined thoroughly (although the GIS-technology has eased the work process). As a result, the reasonableness of using traffic models in the planning process has often been debated.
The Harbour Tunnel project is an early GIS-based assessment of the impacts of a proposed road-tunnel under the harbour of Copenhagen. Besides relying as much as possible on existing models, the study has used a minimum-maximum strategy to search for critical and non-critical traffic components. As an example induced traffic may be difficult to assess, but the 'maximum reasonable induced traffic' could clarify whether it is relevant to consider induced traffic at all. In the same manner recommendations could be given to the need for detailed investigations of e.g. land-use interaction, truck-traffic, detailed route choices, traffic calming, trip distribution and mode choice. A large number of alternatives were examined, several of which could clearly be rejected. In addition, the study provided useful recommenda-tions for a subsequent full-scale modelling study (not yet started). Some of these recommendations were surprising even for experienced modellers.