"ROUGHOMETERS"

Evening Post, Volume CXII, Issue 86, 8 October 1931, Page 11

"ROUGHOMETERS"

CHECKING EOAD SURFACES CONSTRUCTION AND WEAR The days when a smooth road was good enough are over, for the motor vehicle demands a good deal more than. jnst old-fashioned smoothness; the road must be really smooth, not only for the comfort of the passenger, but because high speed vehicles hammer every bump with terrific force and a small irregularity is rapidly turned into m larger one; the hammering increase* again, and the road surface goes to smash. Theoretically, if a perfect surface could be put down, rubber shod' cars and lorries could roar over it yearin and year out, and it would remain as, good at ever. The perfect road is not yet, and probably never will be known; bat it is. the engineer's job, to get as close to perfection as good plans, good materials, and good plant and workmanihip make possible, within, of course, the limits of good finance. Highway! authorities have for many years fixed certain limits of permissible departure from that smoothness on finished surfaces, generally taken by measurement from a straight-edge, say, 10ft long, laid on the surface, but t» check even a mile of surface thoroughly is manifestly impossible, and because each checking is such a task, frequent' tests, necessary if the behaviour of a surface under traffic is to be followed,1 is very much left undone. HOW THE APPAEATUS WORKS. A clever piece of apparatus has now been obtained by the Main Highways Board, and is styled the "roughometer." The principle is very simple. There art three main parts in the roughometer— a vertical steel rod which is -attached to the front axle of the vehicle from which the test is being made, the maim apparatus attached firmly to the engino block (simply because this is most convenient, any other part of the frame would do as well), and a counter on. the dashboard, connected by a flexible steel cable drive with the driving apparatus on the engine block. When a bump in the roadway is hit the springs or the ear give and the vertical rod is thrust upwards in relation to the engine block, apparatus a simple but accurate ratchet (a ball dutch, for those who like to know more of the details) transmits this thrust to the counter on the dashboard, but disregards the recovery aa the rod is running down. The dutch is so finely adjusted, yet so positive in action, that the counter can be sent round slowly, of course, by swaying the car. On the road under test the counter may not be so slow in its spasmodic jumping round. Because the thrust of the vertical rod depends very largely upon the springs of the test car, and also on the speed and the amount of air in the tyres, the results cannot be expressed in. units, but are always relative to other tests made by the same car at the same speed. and these tests are simply transformed into graph form, and the comparative smoothness of ' lengths of the same class of work of .of different types of payment is clearly shown. Thus, in » test run taken, say, from Thorndon to Mungaroa, bitumen laid in summer is contrasted with the same type laid under late autumn difficulties, bitumen. on good foundation would presumably, compare noticeably with bitumen on softer ground, surface sealing would tell a bumpier story, pot holes would send the graph away up, and the penetration job beyond Upper Hutt would provide another comparison. From these graphs.' the engineer can read a great many facts; they; would, of course, have been available to him with the straight-edge test, but the roughometer can count up more bumps in - five minutes than * straight-edge expert can count in a week. IMPROVING STANDARD Or WORK. It Is very much more than an e» gineering toy and has much more than an. academic interest, for the meter quickly gives comparisons of road damage on old surfaces and is a most rapid cheek of the quality of new work. In the. United States, where the instrument wa« evolved by the Bureau of Public Boads, it has been found that roughometer checks have resulted in a, very marked improvement in surfacing work, both as & result of rivalry between contractors to put down the best job they could, and in successive jobs by the same road constructor—the last job might have looked quite good, bat the counter showed up the weak points, and the next job is improved accordingly ' The Main Highways Board has purchased two of these instruments, aEd one, fitted to a standard car, is now being tried about Wellington. It is proving' quite satisfactory, and shortly extensive readings of a number of pavements and other surfaces will be takei