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Show MACHINE MARKS BUMPS IN ROAD Confirms Belie Gravel Can Be Smooth as Pavement in Fair Weather. Records of the number of humps in a mile of road are now being kept by the Minnesota highway department,-according department,-according to a recent bulletin. The record Is made with a "roughnieter," a device attached to an automobile In such a manner that when t lie car strikes a bump which depresses the front springs one inch, one "point" is recorded on the dial on the Instrument Instru-ment panel. Bumps may record from one-thirty-second of a point to two or three points, Many Bumps Recorded. On a recent test run made by O. L. Kipp, construction engineer of the.de-I the.de-I partment, and F. C. Lang, engineer of I tests, one piece of pavement was found on which 528 points were recorded. re-corded. Tills, however, had been built before the state trunk highway system was established and has carried car-ried several thousand vehicles per day for several years. The minimum on pavement was 5G points in a mile, and most of the pavements built hy the state showed from 80 to 150 points per ny'le. Some of this was on new construction, where the expansion joints had not yet been smoothed down. The minimum on gravel was 1U3 points and the maximum recorded was 445, but the latter was on a road so rough that, it was necessary to slow down and dodge around holes. A much higher record would have been made If the average speed of 35 miles per hour had been maintained as was done on the pavement and the better gravel roads. On well-maintained and recently recent-ly leveled gravel road, the "points per mile" usually ran from 150 to IfOO. Smooth Gravel Roads. "The record confirms the popular Impression that some of our gravel roads are 'smooth as pavement,' " Commissioner C. M. Babcock said. "The only trouble is that it is impossible impos-sible to maintain that surface in all kinds of weather or under heavy traffic. We have some gravel roads that cost us more than $2,000 per mile per year for maintenance, and still their condition is far from good. "The abundance of gravel In Minnesota, Minne-sota, however, has made it possible to get the state out of the mud years ahead of some of our neighbor states. There are some states whlcch have much more pavement than we have, but their secondary roads are still mud" roads. In Minnesota these secondary sec-ondary roads, and the trunk highways with lighter traffic, which we cannot afford to pave for many years, if ever, can nevertheless be kept in good condition con-dition in any ordinary weather, and passable in almost any weather." |