They chose a single network solution, with elements of other options

1.15  The results of the Project Definition Study (Figure 6) showed that the Hybrid Option was likely to be the lowest cost option and would cost £1,5334 million (present value), saving £299 million compared to the Zero Option. The Department accepted the study's recommendation that the Hybrid Option should form the basis of the new system, as it was the lowest cost option, involved comparatively low risks, and provided a high level of flexibility.

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4  Although the Hybrid Option formed the basis of the project, the scope changed as the competition progressed, and cost estimates were recalculated over the competition period. So the cost estimates here are not directly comparable with cost and savings estimates arising from the bids or signed contract, discussed elsewhere in this report (Figures 8 to 11 and paragraph 2.34).