The ferries, trams, buses and minibuses in Hong Kong are privately owned and make profits. Against such a background it is understandable that the MeTRo had to be financed on a commercial basis of fares paying for both capital and running costs. This will make it unique.53. The detailed design of underground works is much influenced by the method of construction. Although each contract has 5C100 drawings issued with the tender documents, showing the general arrangement of the required works, the contractor is responsible for the detailed design and working drawings. As detailed drawings are not prepared for the tender the conventional Bill of Quantities is not possible. A method has been developed based on fixed activities which are lump sums for discrete parts of the completed works, and variable activities covering items such as compressed air, ground treatment and different types of tunnel linings which will be ordered by the Engineer. 54.Conditions of Contract were developed from the ICE Conditions and a method of measurement devised based on the above activity concept. The INTERNET project control system is being used so that by estimating the percentage of completion of each activity each month and applying it to the activity, the value of work completed can be determined. The same input to the control system is also used to provide progress reports at intervals as required.55. As an additional source of revenue the space over Kowloon Bay depot is being developed as a commercial venture. A concrete deck will be constructed over most of the depot on which will be built 5000 flats and communal facilities to form a miniature town of 25 000 people. M r P. E. Garbutt, London Transport ExecutiveThe Author has referred in his Paper to London Transport's involvement in the planning of the Hong Kong Mass Transit system in respect of op-erations and layout. We in London Transport feel that we have been able to make a positive contribution to this work.57. Essentially, in the planning of an urban passenger railway, there are three basic factors; the traffic demand, the engineering constraints and the operating requirements. The first two are usually given most attention. Despite the mumbo jumbo that some times surrounds it, the problem of aligning an urban railway to carry the main traffic flows is not one of great difficulty in large and concentrated cities which do not have any existing underground railway lines. The precise level of traffic that will be attracted may be difficult to estimate, but the route that one should adopt is usualiy clear from the

Dr Martin states that on most road construction schemes the main noise problem arises from plant used in bulk earthwork operations. While this may be correct for roadworks undertaken within rural and semi-urban areas, for major urban road construction the noise from piling work is quite often the predominant problem because the noise source in such operations is much closer to inhabited properties than is the case with earthmoving processes.57. Equation (2) indicates that for construction operations which approximate to a line source, the noise attenuation due to the distance between source and receiver (4 is proportional to 10loglo (d/B), where B is the angle subtended by the operation at the receiver. For a point source the distance attenuation is 2O10gl0 d. When the distance d is much larger than the length of the line source the distance attenuation values predicted by the two preceding expressions are the same.According to Dr Martin, when d is less than 60 m the two expressions generate different values of the distance attenuation. However, he does not give any indication of the magnitude of the error which can occur due to treating a line source as a point source, and I was wondering if he has any such data.58. Although the distance attenuation component in equation (2) may be more accurate, for earthmoving operations, than that for a point source, it does require the estimation of an additional unknown factor (i.e., B) for anyone undertaking noise level predictions. In addition, for any quoted value of L,, to be of practical use, the reference distance ( R ) and the angle subtended by the operation at the reference position (4) must be specified. Dr Martin does not quote values of the latter parameter for the data reported in Table 1. Is it possible to obtain this supplementary information?59. With regard to the control of road construction noise, the vital importance of pre-contract estimations must be stressed, as must the roles of the Engineer and the Contractor in combating the nuisance due to construction noise.60. At the design stage the Engineer should make preliminary estimates of construction noise for the projected scheme. The values so derived will only be approximate since at this stage the contractor's construction methods and phasing of work will not be known. However, the noise level estimates will indicate whether the work can be carried out using conventional plant and methods of construction,