COLOMBO STREET OVERBRIDGE

Press, Volume LXXXII, Issue 24901, 14 June 1946, Page 6

COLOMBO STREET OVERBRIDGE

EARLY DECISION TO BE MADE DEPARTMENT OFFERS TO LOWER RAILS Whether or not an overbridge is to be built at the Colombo street radway crossing will be decided by the Christchurch City Council an early date. A decision on this proposal, which has been considered, debated, and then shelved by successive councils oyer many years, must be made before the Railway Department completes its plans for the new Christchurch railway station and for the reorganisation of the lines and' marshalling The reason is that the department has offered to lower the level of its rails by two feet if an overbridge is decided upon. This will lower the deck level of the bridge correspondingly, permit of an easier grade, and —most important consideration of all—shorten the approach ramps at both ends of the bridge in Colombo street and m Moorhouse avenue and Carlyle street by about 3flft in epch case. This, of course, will mean a big saving in cost, both of construction and compensation to property-owners. Once the department completes its plans for the station and track lay-out, however, the level of the rails canpot be changed. Improved Bridge Design The overbridge has not yet been designed, but the department has submitted sketch plans to the council which are regarded as a great improvement on plans considered in former years. The height of the structure will be about 3ft lower than formerly proposed, the extent of the ramps reduced in each direction by about 54ft. The proposed bridge is about 320 ft long, but the length will depend to, some extent on the comparative costs; at the time of cqnstruction of bridging and filling with spoil. The northern ramp will start about two chains north of Moorhouse avenue, and the southern ramp a similar distance south of Carlyle street. As the lower parts of the ramp will be intersected by Moorhouse avenue and Carlyle street, there will tjavp to be slight rises in the road level of both these streets. It is proposed that the bridge itself should be of rigid frame design in reinforced concrete. There will probably be six supporting piers, with the four centre spans each 50ft long and the outer spans 45ft long. The main railway lines in the centre of the bridge will have a clearance of 15ft above the rails, but those on the extreme edge of the crossing, used only tor shunting, will have clearances of only lift 3in.

Gentle Gradient Proposed Over the years there have been many discussions on the most suitable grade for such an overbridge. With the Waltham overbridge the Colombo street structure, if decided upon, will be the only ‘hiH” in Christchurch. Though only about 15ft high, it will be an appreciable obstacle to trams, especially those drawing trailers, to bicycles, and tq the diminishing horsedrawn traffic. Previous arguments about the grade ranged between one in 15 and one in 26. These are comparatively gentle gradients when it is remembered that parts of Dyer’s Pass road have a grade of one in seven. In Wellington or any other city where hills abound, grades of one in 15 or even one in 12 might be accepted for such a bridge. Tentative plans for the Colombo street overbridge, however, provide for a grade of one in 18. The roadway will be the full chain width, and the visibility for traffic will be up to the best highway standards. No finality has yet been reached between the Railway Department and the City Council on the apportionment of the cost of the overbridge if proceeded with.