Quantity of duct and associated works
In order to assess the amount of new duct and associated works required, the following factors need to be taken into account :
the aggregate length of duct required
the opportunities for using existing duct and sharing the duct route with another utility
the opportunities for using alternative "rights of way", for example the MTR or Electric Power tunnels, KCR rights of way, or walkway bridges over congested Central area roads
the duct laying technique, especially the width and depth of trench and speed at which it can be opened, duct laid and re-closed.
In making this assessment, the planning work already undertaken by HCV has been taken into account. On the basis of a detailed planning survey of a specific residential area in Tsuen Wan and less detailed surveys conducted in Mongkok and North Point (judged representative of 1950-75, 1960-80 and 1970-1987 residential development respectively), estimates were made of the ratios between duct and cable lengths required in order to pass every household, and the lengths of public roads in each area.
In assessing how much duct is required for the whole of the cable television service area, BAH has examined the total length of public road in the Territory, as recorded by the Highway Department and thereby determined the length of road which passes residential areas (as opposed to industrial or business areas). Roads in mixed areas with a residential component are included in the total. The rather narrow band of the observed ratio between duct length and road length (1.38-1.44, mean 1.41) in the three sample areas is regarded by HCV as a close relationship typical of the Territory as a whole. It was deduced that 1.41 times the residential road length (as defined above) of duct will be required for a trunk and feeder coaxial distribution system. From our analysis, we conclude that this ratio should in fact be approximately 20% higher (1.7). Our revised estimate captures the increases in ducting required to meet restrictions to building caused by the presence of existing ducts, limited access to roadways or pavements and other building impediments. BAH's calculation yielded a total duct length of 1520 km. This figure does not include "lead-in" duct (that which brings the cable from the street route into the basement or the ground floor of the building to be served). The length of such "lead-ins" which would be under the public road or pavement has been estimated at an average of 12 metres per building served. In high density areas, this would amount to an additional 400 km of under-street duct. Therefore, the total ducting is 1920 kilometres. It should be noted that this figure is approximately 25% below that of the requirements for HKT. This result is not surprising since HKT is using an existing network which has been optimized for telecommunication services, whereas a second network provider is building a new network which is optimized for both telecommunication and cable television services. In the latter case, it is expected that there will be economies of scale in the building of the network.
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