Speed, road surface material and condition, vehicle type and load, and driver reaction time all impact on the distance it takes to bring a car to a stop. Adjusting your driving appropriately can help avoid injury and costly accidents.
The distance it takes to stop a car - the stopping distance - is a combination of how far a vehicle travels during the time it takes the driver to react and apply the brakes, and the distance travelled by the car once the brakes are pressedi.
Impairments on the driver are one of the factors that can have an impact on the reaction distance.
- Alcohol and drugs: Alcohol and drug consumption slows the reaction time sharply when driving above the legal limit of 0.05% blood alcohol concentration, this fact can double the risk of an accidentii.
- Driver fatigue: At 100km/h your car travels 100 metres in four secondsiii. If your reaction is delayed by fatigue it will increase your stopping distance. Fatigue can also result in the disastrous scenario of falling asleep at the wheeliv.
Once a driver does react and hit the brakes, the road surfacei, vehicle type, load and condition, and the speed of the car will impact on the distance travelled once the driver has applied the brakes - the braking distance.
Both the type and condition of the road affect braking distance.
- Unsealed roads, such as those with gravel and dirt, can increase stopping distance as there is less surface tractionv.
- On wet roads, the braking distance increases because you are not able to brake as well as on a dry road, since braking hard can cause your car to skidvi.
The type of braking system impacts on braking distances. Anti-lock brakes (ABS) cars stop better in most hazardous conditions, such as rain, as well as dry conditions, especially at higher speedsvii. The only exception is on gravel roads where stopping distances are increased by an average of 27% compared to non-ABS vehiclesvii.
However, according to a recent Monash University Accident Research Centre studyviii, the development of anti-lock braking systems hasn’t reduced crashes in the real world significantly, a fact attributed not to ABS advances but to drivers adjusting behaviours to the capabilities of ABS technology.
The load on the vehicle, including towing a trailer, boat or caravan, also increases stopping distanceix. 4WDs also require longer stopping distances, as they generally weigh more than non-4WD vehiclesx. To reduce the risk of an accident due to load, increase the gap between you and the vehicle in front.
Keeping your car in good condition is also important. According to the national Canstar Blue Survey, 800,000 drivers, Australia-wide, let their tyres wear out to risky levels that can cause serious accidentsxi. Tyres should be checked regularly for wear, tear and correct inflation. When necessary they should be replaced.
Speed is the "biggest killer on our roads"xii and has a big impact on stopping distancesxii. Higher speeds increase the stopping distance, which greatly heightens the risk of an accident. In addition to the reaction distance being greater at speed, braking distance is increased significantly. For example, the braking distance of an average-sized car increases by 11m when the speed goes from 60km/h to 70km/hxiii. This is one of the reasons it is essential to keep an appropriate gap to the vehicle in frontxiv.
By taking into account the factors that influence stopping distances, and driving appropriately, you can minimise the risk of rear-end and other emergency braking-related accidents. Unfortunately, not all drivers do this, so taking out car insurance can protect you in the event of poor driving by other road users.
i Centre for Accident Research & Road Safety, Queensland Government, 2011, State of the Road: Speeding, http://www.police.qld.gov.au/Resources/Internet/news%20and%20alerts/campaigns/fatalfive/documents/speeding_fs.pdf, p.2.
ii Centre for Accident Research & Road Safety, Queensland Government, 2012, State of the Road: Drink driving, http://roadsafety.transport.nsw.gov.au/stayingsafe/fatigue/index.html
iii Roads & Maritime Services, New South Wales Government, 2011, Driver fatigue, http://roadsafety.transport.nsw.gov.au/stayingsafe/fatigue/index.html
iv Centre for Accident Research & Road Safety, Queensland Government, 2011, State of the Road: Fatigue, http://www.police.qld.gov.au/Resources/Internet/news%20and%20alerts/campaigns/fatalfive/documents/fatigue_fs.pdf
v Roads & Maritime Services, New South Wales Government, 2006, Road environment safety, http://www.rta.nsw.gov.au/roadsafety/downloads/road_environment_safety_practitionersguide.pdf
vi Department of Transport, Western Australia Government, 2012, Part 3: Major Road Rules and Additional Safety Advice, 8 January 2013, http://www.transport.wa.gov.au/mediaFiles/LBU_DL_B_DriveSafePart3.pdf
vii Royal Automobile Club of Victoria, 2004, Effectiveness of ABS and Vehicle Stability Control Systems, http://www.monash.edu.au/miri/research/reports/other/racv-abs-braking-system-effectiveness.pdf
viii Scully, J. and Newstead, S. 2007, Preliminary evaluation of electronic stability control effectiveness in Australasia, http://www.monash.edu.au/miri/research/reports/muarc271.pdf
ix Department of Transport and Main Roads, Queensland Government, 2013, Safe Towing: All about safe towing, http://www.tmr.qld.gov.au/~/media/Safety/Vehicle%20standards%20and%20modifications/Loads%20and%20towing/Safe%20towing/Safe_towing_guide.pdf
x Australian Transport Safety Bureau, Australian Government, 2004, Road Safety in Australia: A Publication Commemorating World Health Day 2004, http://www.infrastructure.gov.au/roads/safety/publications/2004/pdf/Safety_Aust.pdf
xi Dowling, N. 2012, Gen-Y drives on unsafe tyres, http://www.carsguide.com.au/, http://www.carsguide.com.au/news-and-reviews/car-news/gen_y_drives_on_unsafe_tyres
xii Roads & Maritime Services, New South Wales Government, 2012, Speeding, http://www.rta.nsw.gov.au/roadsafety/speedandspeedcameras/index.html
xiii Department of Transport and Main Roads, Queensland Government, 2013, Stopping distances, http://www.tmr.qld.gov.au/Safety/Driver-guide/Speeding/Stopping-distances.aspx
xiv Roads & Maritime Services, New South Wales Government, 2012, A guide to the Driving Test, http://www.rms.nsw.gov.au/roads/licence/index.html, p.3.