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Road maintenance and construction. Hossein Naraghi CE 590 Special Topics Safety March 2003. Time spent: 6 hrs. Pavement condition. Pavement condition includes Resistance of the pavement surface Important in crash terms Roughness of the pavement Important in terms of economic efficiency
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Road maintenance and construction Hossein Naraghi CE 590 Special Topics Safety March 2003 Time spent:6 hrs
Pavement condition • Pavement condition includes • Resistance of the pavement surface • Important in crash terms • Roughness of the pavement • Important in terms of economic efficiency • Effects on vehicle operating costs • Road maintenance activities which involve resurfacing may be directed at either friction or roughness, or both
Pavement condition (continued) • Skid resistance • Skidding is a contributory factor to many crashes • On wet roads • On approaches to intersections • Crashes which occur in wet weather typically • Occur at 2 to 3 times the rate of crashes in dry weather, all else being equal • Represent about 20-30 percent of total crashes • Involve skidding • In up to 70% of cases, improving skid resistance may be helpful
Pavement condition (continued) • Skidding crashes include • Rear-end • Run-off-road • Sideswipe • Head-on • Pedestrian • Coefficient of friction • Above 0.55 is usually enough to significantly reduce braking and turning crashes
Pavement condition (continued) • Frictional resistance can be substantially improved by • Providing a suitable road surface texture • Overlay of high friction asphalt • Grooving/grinding an existing surface • The need for such a treatment can assessed by measuring friction using skid resistance machines
Pavement condition (continued) • Moisture presence has • Little effect on skid resistance at low speeds • Much higher effect at higher speed • As speed increases the water must squeeze away from the surface before the tire can grip • Hydroplaning s more likely at higher speeds • Tire does not develop full grip over an area because of the presence of a film of water about 6 mm thick
Pavement condition (continued) • Splash and spray which associated with crashes occurrence • Related to heavy vehicles on wet roads • Can be reduced through the use of open-graded or porous asphalt • This is much less noisy than regular asphalt or concrete surfaces • Mainly controlled through on-vehicle devices
Pavement condition (continued) • Considerable attention has been given to the effects of road roughness on vehicle operating costs and to the economic efficiency of road provision and optimum maintenance intervention levels • Less attention has been given to safety aspects of road roughness • Might be due the reason that in developed countries at least, roads are maintained at a sufficiently high level that roughness does not become a safety issue
Pavement condition (continued) • Surface roughness is a much larger factor in truck crashes and motorcycle crashes than in car crashes • An Australian study of truck crashes found that 10.7% of such crashes associated with drivers losing control due to potholes • Some cases in US reported failure of a mechanical component of the truck was due to pavement roughness • Another study found that rough surfaces can cause load shift in large trucks, or rollover or both
Pavement condition (continued) • It seems reasonable to suppose that • Irregularities or defects in the road surface could adversely affect the ability of driver to control the vehicle • There is a little research on the subject • In developed countries this factor affecting only a small percentages of crashes • This factor is affecting a more significant percentages of truck crashes
Pavement resurfacing • Pavement resurfacing may be undertaken as part of an crash-related mass action program or part of routine pavement maintenance • The potential effect of resurfacing on safety is a result of two factors working in opposite direction • Since resurfacing reduces surface roughness and improves ride quality, it may lead to increase in average speed • Resurfacing often increases pavement skid resistance, which reduces stopping distance and improves vehicle controllability when pavement surface is wet
Pavement resurfacing (continued) • Safety effects of resurfacing • Routine resurfacing of rural roads increases dry weather crashes by 10% • Increased speeds • Dry weather skid resistance and stopping are unaffected by resurfacing unless the original pavement was extremely rough • For most rural roads, the net effect of resurfacing on crash rate is small and gradually diminishes over time
Pavement resurfacing (continued) • Resurfacing improves the safety performance of roads that experience an abnormally high frequency of wet weather crashes • Resurfacing provide opportunity to correct deficient pavement cross slope at little or no extra cost • Correcting cross slopes allows better drainage of the pavement surface and improves vehicle control in wet weather • Careful attention to removal of surface defects and necessary improvements to skid resistance, surface drainage and superelevation may help to offset the adverse effects of increased speeds
Work zones • Data from US suggests that work zones are hazardous from a road safety viewpoint • Sites showing the worst increase in crashes were short duration • Short term construction zones perhaps reflecting driver expectancy or poor road work signing, or both • Heavy vehicles face particular difficulties at work zones include • Median crossovers • Reduced number of lanes • Reduced lane widths
Work zones (continued) • Being required to travel closer to potential hazards • Excavations • Drop-offs • Short merge zones • Flashing signals • Which are at truck driver’s eye height causing visibility problems • All these mean explicit consideration should be given to warning, delineation and control devices for trucks at work zones
Work zones (continued) • Principles involved in safety and effectively controlling traffic at work zones • Traffic safety should be an integral and high priority element of every construction job, from planning, through design, to construction • Construction and maintenance operations should inhibit traffic as little as possible • Clear and positive guidance must be provided to drivers approaching and traversing work zones
Work zones (continued) • Routine inspection of traffic control elements is essential to ensure acceptable traffic safety and operations • Appropriate training of all relevant personnel is essential • Adequate legislative authority for implementation and enforcement of traffic regulations applicable to work zones • Maintaining good public relations, and keeping the motoring public informed is essential
Work zones (continued) • Organization for Economic Cooperation and Development has developed the following guidelines for traffic management at work zones • Capacity restriction must be carefully evaluated and monitored • Lane closures should normally start from the fast lane • Buffer zones should be provided wherever possible • Incident control is important, especially with contra-flow techniques • Speed limits should be realistic, should be supported by appropriate accompanying measures and not rely solely on signing