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Science Road Safety Science Adverse Weather Can Create Dangerous Driving Conditions D D N N A Science Road Safety SCIENCE A TECHNOLOGY N and I I ACTION THIRDSECOND EDITION EDITION D D N N A Science Road Safety SCIENCE A TECHNOLOGY N and I I ACTION THIRDSECOND EDITION EDITION Every year some hundreds of people are killed on the roads The estimated stopping distance for Pat’s car, assuming a response in Ireland – about one a day on average. Awareness campaigns time of say 2 s and a coeffi cient of friction of 0.4, would be 107 m. have not produced the desired change in driver behaviour. Drivers are advised to leave at least a ‘three second’ gap between cars. An understanding of the factors that are common to many In three seconds a car travelling at 80 km/h covers 66 m and at that speed it would require a very fast response time (1 s) and a high road accidents and an understanding of the laws of motion coeffi cient of friction (0.9) to bring a car toThe an unanticipatedestimated stopstopping within distance for Pat’s car, assuming a response mayEvery help yearincrease some awareness hundreds of the ofdangers people and are encourage killed on the roads 50 m. These estimates do not take account of brake engagement time youngin Ireland people – aboutto take onegreater a day care on on average. the road Awarenesswhether as campaigns which is about 200–300 ms. time of say 2 s and a coeffi cient of friction of 0.4, would be 107 m. pedestrians,have not cyclists,produced passengers the desired or drivers. change in driver behaviour. Drivers are advised to leave at least a ‘three second’ gap between cars. Tyre infl ation An understanding of the factors that are common to many In three seconds a car travelling at 80 km/h covers 66 m and at that Reaction time (normal reaction time): The frictional force between two surfacesspeed depends it wouldon the materialsrequire a very fast response time (1 s) and a high road accidents and an understanding of the laws of motion involved and on the force between them. Contrary to expectation, it The average time for coeffi cient of friction (0.9) to bring a car to an unanticipated stop within reactionmay helpto visual increase stimuli awareness of the dangers and encourage does not depend on the contact area – at least not directly. In the (with no choices) is case of a car, the force between the surfaces50 m. is Thesethe weight estimates of the car, do not takeThe account National of brake Car engagement Testing Service time betweenyoung 180 people and 200 toms take greater care on the road whether as distributed over the four wheels. If the wheelswhich are is very about narrow 200–300 then the ms. Since January 2000 all cars four years and older in Ireland must weight of the car presses on a small area. The frictional force remains (0.18–0.20pedestrians, s). In the cyclists, case passengers or drivers. undergo a test called the National Car Test [NCT]. This test was of auditory stimuli it is Fig. 3 Adverse weather can create dangerous driving conditions. the same but it is transferred through a small amount of rubber. A large introduced to improve road safety, to reduce harmful emissions shorter (140–160 ms). When frictional force is then more likely to exceedTyre the internal infl forcesation holding and to comply with the EU Directive 96/96/EC which makes car the rubber together and bits of the tyre are worn off. For this reason decisions are required the the tyres and the road; when this happens the car cannot be steered and testing compulsory in all EU member states. timeReaction required to make time an (normal reaction time): wider tyres are desirable. The frictional force between two surfaces depends on the materials the stopping distance increases. Following a competitive tender process, the SGS Group was appropriate response to a involved and on the force between them. Contrary to expectation, it The average time for Over-infl ation of tyres reduces the area of contact with the road and the awarded the contract to operate and manage the car testing visual stimulus increases Kinetic energy (E ) = ½m v2 reaction to visual stimuli k tyre is more likely to be abraded by friction.does notUnder-infl depend ation makeson the contactservice area in– Ireland.at least NCTS not directly.now operates In the 43 Test Centres with age from about 370 Work done = frictional force × distance = F × s steering more diffi cult. case of a car, the force betweenthroughout the surfaces the country. is the The weight SGS Group of the is the car, largest inspection,The National Car Testing Service ms,(with for 20–30 no year choices)olds, to Fig.is 1 Scene of a crash – a common Frictional force is equal to the coeffi cient of friction multiplied by the testing and verifi cation company in the world. occurence on Irish roads Higher speed reduces traction (grip on distributedthe road) and over increases the four the wheels. If the wheels are very narrow then the Since January 2000 all cars four years and older in Ireland must aboutbetween 440 ms 180 for and60–70 200 ms weight of the car: F = µ × mg year(0.18–0.20 olds. s). In the case probability of aquaplaning in wet conditions.weight of the car presses on a smallAlthough area. this The lesson frictional has been force about remains braking, the NCTS testsundergo a test called the National Car Test [NCT]. This test was In the case of cars that are in good working order travelling on a dry road all physical aspects of car safety: wheels, tyres, lights, of auditory stimuli it is Fig. 3 Adverse weather can create dangerous driving conditions. the same but it is transferred through a small amount of rubber. A large introduced to improve road safety, to reduce harmful emissions Other factors that affect reaction time are: the coeffi cient of friction (µ) ranges from about 0.6 (for ordinary cars) to Alcohol frictional force is then more likelysteering, to exceed electrical the internalsystems, forcesmirrors, holding fuel systems etc. Theand to comply with the EU Directive 96/96/EC which makes car • shorterthe complexity (140–160 of the ms). situation. When about 0.95 (for the most expensive cars). standards for exhaust emissions for both petrol and diesel decisions are required the Internationalthe rubber studies together of the effects and bits of theengines tyre are are designed worn off. to Forminimise this reasonthe harmful effects oftesting compulsory in all EU member states. In braking E the= F tyres× s and the road; when this happens the car cannot be steered and of alcohol on driving show • timethe illuminationrequired (dim to situationsmake an require more time to more interpret). k wider tyres are desirable. atmospheric pollution. ½ m v2 the= (µ stopping × mg) × s distance increases. signifi cant impairment of Following a competitive tender process, the SGS Group was • appropriatea driver’s general response level of alertness. to a 2 attentiveness, visual function, The NCTS employs about 450 people in vehicle inspection, Therefore s = v /(2 × µ × g), 2 Over-infl ation of tyres reduces the area of contact with the road and the awarded the contract to operate and manage the car testing visual stimulus increases Kinetic energy (E ) = ½m v perception and choice reaction customer service, technical and administrative roles. • normal but unexpected events (e.g. brake lights on the car ahead). k tyre is more likely to be abraded by friction. Under-infl ation makes service in Ireland. NCTS now operates 43 Test Centres with age from about 370 where g is the acceleration Work due to done gravity. = frictional force × distance = F × s time (the time required to • unusual and unexpected events (e.g. car approaching on the wrong choosesteering a response more to diffi a complex cult. throughout the country. The SGS Group is the largest inspection, ms, for 20–30 year olds, to Fig. 1 Scene of a crash – a commonThis shows that the braking distance (s) is proportional to the speed side of the road). Frictional force is equal to the coeffi cient of friction multiplied by the situation) when blood alcohol testing and verifi cation company in the world. occurence on Irish roads squared (v2); e.g. doubling the speed increases the stopping distance by about 440 ms for 60–70 contentHigher (BAC speed) is 10 mg/100reduces mL traction (grip on the road) and increases the • blood alcohol level, which is a factor in about 33% of road accidents, a factor of four. The massweight of the of carthe is car: not aF factor.= µ × For mg an ordinary car year olds. (0.01probability g/100 mL, of0.01% aquaplaning g/mL or in wet conditions. Although this lesson has been about braking, the NCTS tests increases reaction time and impairs judgement. travelling at 100 km/hour (27.8 m/s) the braking distance would be about 0.1 g/L). Consumption of one 55 m; this does not takeIn accountthe case of theof cars driver’s that response are in timegood. working orderFig. travelling 4 Every year on more a dry then road300 all physical aspects of car safety: wheels, tyres, lights, ManyOther studies factors have thatshown affect that 95% reaction of real responsetime are: times of drivers are people are killed on our roads. standard drink raises the BAC by the coeffi cient of friction (µ) ranges from about 0.6 (for ordinary cars) to steering, electrical systems, mirrors, fuel systems etc.
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