HIGWAYS BOARD WORK

Hokitika Guardian, 31 March 1930, Page 7

HIGWAYS BOARD WORK

ELEVATION AND WIDENING OF CURVES.

WELLINGTON, March 27. Motorists who are content to appreciate the improved road surfaces provided through the expenditure of the tyre and petrol taxes under the dilection of the Main Highways Board wiil probably not as a rule realise that aiiotuer highly important development is being encouraged, to bring the roads into line with the requirements of a reasonably high speed. Super-elevation of curves and widening of such points is being carried out as a definite policy, and the Main Highays Board, to encourage the alterations to existing surfaced highways, has indicated to the District Highway Boards and all local au critics ilueieslcd that it is prepared to subsidise such improvements on the same basis as maintenance, namely £2 lor £l. Super-elevation on curves is an old practice on railways, and how that the average speed of road vehicles approximates to that of the average train, it becomes highly important to build curves which will counteract the tendency to run off the track at such points. The degree of super-elevation required depends cm speed and the severity of the curve, and having these factors in mind, the Main Highways Board has prepared for the guidance of road enginers and constructors a complete explanation of the best methods to be adopted. The engineering formula, set out in a. clearly, designee graph, will not interest the genera! reader, but lie might be able to note the curve improvements by having the knowledge that some of the reeommemlated degrees of super-elevation as follows: !

Curves up to two chains .radius: 11 inches per foot super-elevation.

Curves from sixteen chains'radius to forty chains radius: half an 'iilcli per foot Super-elevation. ,\VV These examples range fromlthe difficult curve to one •which the would certainly npt regard as;, 'calling for greatly slackened speed. - The .Main Highways Board is recommending that the super-elevation should be ’' 'carried on for at least two feet on cither side of the surfacing,, on the road shoulders, aikl it is prepared to assist.financially iii a further width. of surfacing and formation on curves to the extent of five-feet on the inside of a three chain curve, no. to ten feet inside, such a sharp curve as one of two , cnains 'radius.