§ Mr. Pawseyasked the Secretary of State for Transport what is the cost per motorway mile of a concrete carriageway; and how that compares with tarmac.
§ Mrs. ChalkerIt is not possible to make a simple comparison between concrete and bituminous carriageways in terms of cost per mile, because the relationship between them changes according to the location of particular sites and the nature of aggregates available in the locality.
Tenders are normally invited for both forms of construction and the contract awarded on the basis of the lowest cost. Recently the mileage of new trunk road construction has been approximately equally divided between the two types of pavement.
§ Mr. Pawseyasked the Secretary of State for Transport what is the estimated life of a concrete motorway compared with tarmac.
§ Mrs. ChalkerThe life of a carriageway is expressed in terms of accumulated axle loadings that it is designed to withstand before major structural rehabilitation or strengthening will be required. Concrete pavements are designed to withstand accumulations of axle loadings over a 40-year period, whereas flexible pavements, which are surfaced with bituminous materials, are designed to withstand axle loadings over a 20-year period.
Pavement design is not amenable to precise calculation because of uncertainties inherent in the assumptions that have to be made about the nature of the ground it is built on, construction problems and the traffic carried. In practice, these design loadings might be exceeded or not achieved by quite wide margins.