Design, Construction

Press, Volume CVII, Issue 31502, 17 October 1967, Page 21

Design, Construction

The design of the new northern motorway provides for six lanes between Chaneys Corner and the Cam Road, which is on the northern side of Kaiapoi. At this point, Rangiora, northern Kaiapoi and certain beach traffic is filtered off, and only four lanes require to continue north.

In the first instance, however, only four lanes will actually be built as far as Cam Road, and two lanes will be built on to Pinehaven. A wide median strip will be left, and this will provide the necessary width for the other two lanes to be provided when needed. An interchange has already been built at Tram Road and further ones will be constructed at Chaneys, Ohoka Road and Cam Road to give an average spacing of one and a quarter miles. At Chaneys a “Y” type interchange will bring together the present main city outlet (the Main North Road through Belfast) and a subsidiary outlet (Marshlands Road) until they can be replaced by higher standard roads. The Christchurch Master Transportation Plan provides for the former to be replaced by the Belfast by-pass (to serve the airport and the western suburbs) and the latter by the northern out-

let (from the city centre to serve the suburbs of the north, south and east).

In the construction of the motorway, the standards used have been for a design speed of 70 m.p.h., a maximum grade of 1.67 per cent, a lane width of 12ft, and a median width of 20ft, including two paved shoulders 4ft wide for the section of four-lane motorway, and 6ft wide for the six-lane motorway.

The standard for the width of the outer shoulders is 10ft, including 3ft of paved shoulder, and the side or batter slopes up to 10ft from the shoulder are on a four to one slope, from 10 to 20ft are on a three to one slope, and 20ft and more from the shoulder are on a two to one slope.

On-ramps will have a one in 50 taper, and a 50 m.p.h. design speed at motorway terminals. The maximum grade is 5 per cent Off-

ramps have one in 12 taper, and 50 m.p.h. design speeds. Again the maximum grade is 5 per cent. Special attention is being given to the aesthetics of the motorway, and a feature of note at present is the special 10 in one sloped batter on the south side of the Train Road deviation. The approach ramps to the new Tram Road bridge blend into the countryside and have been returned to agriculture. On the north side, tree planting will be used to soften the contours on the steeper batters. The bridge to carry the motorway over the Waimakariri River is a twin structure, each bridge having 30ft between guard rails at the four-lane stage and 42ft at the six lane stage; 80ft pre-stressed concrete spans are used and the bridge length is about 1380 ft. The other motorway bridges (Adderley Terrace, railway, Kaiapoi River, and Cam River) are likely to be single structures when fully developed, and will have 12ft lanes, 6ft shoulders and a median as for the motorway proper. Bridges to carry Tram Road. Ohoka Road and a deviation of Cam Road over the motorway have been designed to suit the individual needs of the local roads. From the motorway, however, they will appear identical.