Questionnaires about the rate of windscreen breakage on new surface dressings on heavily trafficked roads (mostly rural) were sent in march 1971 to selected county authorities. An analysis of data received from eleven counties shows the extent of the problem. The greatest number of breakages occurred in the first week after laying the dressings and the total was independent of the size of the chipping used within the range 11 mm to 12.7 mm. Approximately three windscreens were broken for every 100,000 vehicle kilometres during this first week. In the next three week period the rate of breakage was 0.41 and thereafter was little different on the sections which had been dressed from that on untreated roads (some 0.33 breakages for 100,000 vehicle kilometres). Significantly higher rates of breakage were found on surface dressed sites longer than 3 km than on shorter sites. No conclusive evidence was found to suggest improved performance with either lightly coated or uncoated chippings. Contrary to expectations, lower levels of windscreen breakage were found on sites where steel-tyred rollers were used in preference to rubber-tyred rollers. The effect of using steel-tyred rollers on surface texture depth (an important factor in maintaining resistance to skidding at high speeds) requires further investigation. (Author/publisher)
Abstract