A preliminary study has been made to obtain information on the broad breakdown of the price of driven-tunnel construction. Only the direct engineering prices of construction are discussed and non consideration is given to any indirect costs or benefits associated with sub-surface roads. For seven road tunnels built in the United Kingdom since 1956 wide differences in total price were found, depending largely on the prevailing ground conditions. The most expensive tunnels are the sub-aqueous ones constructed through mixed-ground conditions; such work would constitute only a small part of urban road systems. At 1968 contract rates the overall price of a single tunnel carrying a 7.30-metre-wide carriageway ranges from about £2 million to £9 million per kilometre, ignoring the price of portals, interchanges and the like. The excavation and primary lining was the most expensie portion of the works in all the projects considered and amounted to £6.0 plus or minus 2.0 million per km for the cast-iron-lined tunnels in very difficult ground conditions and £1.2 plus or minus 0.4 million per km for those lined with concrete in less rigorous conditions. The prices of the secondary components for these two situations were £0.8 plus or minus million per km and £0.3 plus or minus 0.2 million per km respectively. The expenditure on services with one exception (£0.1 million per km) showed little varation from one project to another, amounting to £0.8 million plus or minus £0.2 million per km. (A)

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