BIGGEST BRIDGE IN THE WORLD.

Dunstan Times, Issue 3131, 21 August 1922, Page 7

BIGGEST BRIDGE IN THE WORLD.

The longest, bridge' in the world: is the 'Pay bridge in Scotland, which; i» two miles and seventy-three yards from end to end; but a bridge more than twice a» long as this is to be built at San Francisco. As this bridge of five miles is to cost about £10,000,000, and money is difficult to get just now, it ; s not to be started immediately The scheme has just been madb publie. It is wonderfully conceived, and the way in which the various difficulties have been overcome is regarded as a .stroke of engineering genius. San Francisco, like other big eities, is growing all the time, and vast suburbs, which a.re really large towns in themselves, have sprung up across the bay. They are Oakland, Alameda, and Berkeley, 'and the bay at tins point is four miles wide, so that ail the business men and others who cross to San hiraucisco every day have to do so on large ferry boats. Such methods of access to the main part of the city, where huge numbers of people and many vehicles are concerned, means great delay, and the need for a bridge has long been recognised. Forty million passengers and nearly three-quarters of a million vehicles cross on the ferry boats every year. So urgent is the need that the city authorities last year asked Mr J. V. Bavies and Mr Ralph Modjeski, two distinguished engineers, to make a survey and report upon the possibility of a bridge and its approximate cost. The engineers carried out their work promptly, and have just reported that it is quite possible to build a bridge that shall link up San Francisco with the outlying towns and suburbs across the bay. The greatest difficulty they had to contend with was the keeping open of a waterway for large and small vessels across the line of the proposed bridge to the inner part of the harbor. With such an important channel and so busy a bridge no system of bascules, as at the Tower Bridge in London, was possible, but the engineers surmounted the difficult in an ingenious way. They propose to end the bridge before it reaches the shore on the San Francisco side, and to continue it for threequarters of a mile as a tunnel, sloping down at each of its ends till the centre part, has a depth of forty feet of water above it, over which the largest ships could pass to and fro. From the end of the tunnel where it comes up in the harbor there will be a girder bridge nearly two and a quarter miles long, then a pile trestle continuation for three-quarters of a mile, and a mole, or embankment, rising out of the water for another two and a. quarter miles, so that the whole way from shore to shore will be nearly six miles. The girder part of the bridge will have forty great spans of about 300 feet each, carrying two railway tracks and a roadway forty feet wide. The tunnel will consist of two single track railway tubes and one tube for vehicles with a roadway twenty feet wide. Where the tunnel joins the girder bridge in the harbor there will be a lighthouse and a ventilating plant to blow fresh air into the tubes. It is a gigantic scheme, the biggest thing ever conceived in connection with bridge-building. It will take four years to build, and the engineering world is looking forward with the keenest interest to its accomplishment.