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Factors causing crashes include alcohol, drugs, using mobile phones while driving, fatigue and not stopping at red lights. One of the most frequent causes of fatal crashes is speed.
Speeding may not even mean travelling over the speed limit, but driving too fast for prevailing conditions, such as the weather, vehicle, road, light, traffic and, of course, the driver.
Speed limits warn people to slow down before sharp curves or hazardous sections of the road. If everyone travelled at the correct speed, it would be easier for drivers to judge closing distances and understand what other drivers intend to do.
Speed and vision
The faster you go the less clearly you focus on things. This makes your distance judgment increasingly inaccurate and multiplies your chance of a collision. In addition, your field-of-vision is reduced, meaning you may miss seeing objects approaching from the side or rear.
Speed and darkness
From dusk onwards your sight has to adapt to changing levels of brightness. Your eyes get confused by a sky that is still light, a darker road, deeper shadows, less contrast in colours and lights from oncoming vehicles and roadside signs.
With full darkness many of the 'cues' drivers depend on in daylight are eliminated. Vision is restricted to a relatively small area illuminated by the headlights. Because of this, it's more difficult to make accurate judgements due to the shortened visible distance ahead.
The faster you go, the harder you hit. When a vehicle brakes, the speed reduction can be smooth and progressive. However, in a collision the energy is absorbed in the crumpling of the vehicle's components and the object it strikes, in a fraction of a second.
The impact of a collision at 50km/h is the equivalent to a vehicle falling from a three storey building, with you in it. Double the speed to 100km/h and prepare for the equivalent of a 12 storey drop.
Speed and stopping distances
The faster you go, the longer it takes you to stop. That's not taking into account driver reaction time and the effects of fatigue, alcohol, drugs etc.
Speed enforcement signs in Australia are erected in accordance with national standards. In Western Australia, the agency responsible for determining the speed limit is Main Roads W.A. (MRWA) The speed limit in any particular area is determined by Engineers and based on a number of factors including the general topography of the location, the urban density and road design.
Apart from the commencement and end of a speed zone signs, MRWA erects 'repeater' or 'additional' speed signs further along the route within the zone. That authority endeavours to space them as follows and some variances do occur, but distances are not bound by legislation:
- 60 kph and 70 kph zones – signs 1.0 km apart
- 80 kph and 90 kph zones – signs 1.5 km apart
- 100 kph and 110 kph zones – signs 4.0 km apart
A prudent driver when travelling along, or entering upon another carriageway would reduce a vehicle's speed to the speed permitted in a 'Built Up Area' namely 50 kilometres per hour and not increase speed until another speed sign is observed. It is fraught with danger to presume that a particular road may have a speed limit applied to it because of other roads in the area.
The speed limit in the Perth CBD is 40 kph and does not change.
40 kph on school days
7:30–9am and 2:30–4pm (or as per signage)
40 kph speed limit takes effect from the sign and ceases at the End of School Zone sign.
Vehicle fog lights
Be considerate of other drivers and only use fog lights in fog or adverse weather. TURN OFF fog lights in fine weather.
There is a $100 fine and 1 demerit point for inappropriate use of fog lights.
See the Department for Planning and Infrastructure's Drive Safe handbook for more information including:
- Safe driving
- How to obtain a Western Australian Licence
- Road rules
- Emergencies and crashes
- The law and you
- Ride safe