SCIENCE JOURNAL 2018

Environmental Factors on Speed, Reaction Time & Breaking Time The environment and area someone drives in plays a big part in determining the survival or death of a crash victim. If a car is travelling at high speeds in a residential or metropolitan area, it is very likely that some sort of collision would occur. However, a similar problem arises in rural areas; most rural areas have high speed limits due to little roadside activity, but this means that when an accident does occur it is more likely to be fatal. Statistics show this, as, according to Transport NSW, most metropolitan crashes occur at speeds of around 50km -1 & 60km -1 , whereas most crashes occur in rural areas at around 100km -1 (Transport for NSW, 2015). As well as this, if the car is going up or down a hill, braking times could be longer, with another variable being what material the road is made of (this is mainly a variable in rural areas, as dirt and gravel roads do not have good traction (Arrive Alive, 2018)). Thankfully, the government does do its best to resolve these problems. All roads surrounding schools in Australia classify as ‘School Zones’, where, between 7-9 am and 2-4 pm, all motorists must slow down 20 or 30 kmh -1 for 200m to reduce the risk of car accidents involving students and parents (Department of Transport and Main Roads, 2018). Also, many car parks, drive-throughs and educational areas have speed bumps: humps in the road that make drivers reduce their speed (as if they travelled over them quickly the car would become airborne) (Speed Humps Australia, 2018). Roundabouts have also been proven to be safer for drivers rather than traditional intersections, showing a 37% reduction in overall collisions, as they can be less confusing and requires cars to travel at lower speeds (Washington State Department of Transportation, 2018).

the driver’s reaction time depends on the speed of the car. According to the Transport Accident Commission (TAC), and calculated using equations 1 & 2 from the Appendix, the reaction time of a driver is typically around 1.5 seconds. Nonetheless, the distance travelled during the reaction & braking time depends purely on the speed of the car (TAS, 2018). These statistics are shown in more detail in Figure 2, which details the stopping time & distance of a car at different speeds. The graph shows that an object would get lightly touched when a car is travelling at 60kmh -1 , but any faster than that would cause a collision with the object.

Figure 2: Statistics on reaction & breaking distance & time (TAS, 2018). When the car hits an object, depending on the weight of the object, either the car’s speed will transfer in a very short time to the object, or the car will crash into the object and the momentum would cause rapid movement to the people in the car. As an example, from the data in the graph, we can tell that a car travelling at 65kmh -1 would hit an object at 32kmh -1 . If the object was a young boy, the time taken for the boy to be travelling at the same speed as the car (32kmh -1 , or 8.2ms -1 ) due to impact would be about 0.024 seconds (if he was 20 cm thick) (refer to equation 3), meaning he would accelerate at around 340ms -2 (refer to equation 4). If the boy weighed 50kg, the force applied on him would be around 17,000 Newtons (refer to equation 5), an extremely large amount of force to be exerted on a young boy, almost guaranteeing his death (Fletcher, 2015).

SC J SI

21

Somerset College Journal of Scientific Issues

Year 10