Speed is at the very heart of road safety. It affects both the risk of being involved in a crash and the outcome should a crash occur. Put simply, reduced speeds reduce the force of impact.
Speed contributes to your stopping distance when braking suddenly, and to the severity of impact if a crash occurs. Put simply, reduced speeds reduce the force of impact.
Last year alone, 32% of fatalities on our roads were from speed related crashes, with 47% in 110km/h zones, followed by 12% in both 60km/h and 70km/h zones.
A SPEED LIMIT IS SET TO REDUCE THE ROAD SAFETY RISK TO USERS, REDUCE CONGESTION AND MAXIMISE TRAFFIC FLOW. IT IS DETERMINED BY TRAFFIC VOLUME, CRASH RISK AND TRAFFIC MIX. THE NUMBER OF DRIVEWAYS AND PROXIMITY OF SCHOOLS ARE ALSO CONTRIBUTING FACTORS.
Physics of Speed
REACTION + STOPPING DISTANCE
The speed you’re travelling at affects your reaction time and stopping distance if you need to brake or manoeuvre suddenly.
That’s the distance you travel by the time you react, and the distance you travel once you brake.
But that’s not the only factor – driver and road environment also play a part.
For example, a distracted or tired driver will take longer to react, and wet road conditions will make a car travel further when braking.
On a dry road, an average family car driving at 70km/h will travel 29+ metres before reacting and an additional 27+ meters before coming to a complete stop.
On a wet road, the same car, at the same speed will travel an extra 13 metres.
If you’re in a crash, your speed determines the force of impact you experience when you collide.
So, an impact at 80km/h will be far more forceful than an impact at 50km/h and greatly reduces your chance of survival.
Vehicles don’t have to be going fast to cause harm.
Many fatalities occur at lower speeds, especially when pedestrians or bike riders are involved.
A person walking has a 90% chance of survival if hit at 30km/h, but only 50% chance of survival if hit at 45km/h.
The human body has next to no chance of surviving an impact above 80km/h.
Selecting a Speed
Responsible drivers and riders select the appropriate speed to travel for the conditions around them.
So, if driving conditions change, it’s up to you to adjust your speed accordingly, within that limit.
Speed choices are influenced by a number of factors:
- THE ROAD + VEHICLE
- Road layout, surface quality (e.g. unsealed road), wet/icy roads, vehicle condition/age
- THE TRAFFIC ENVIRONMENT
- Speed of other road users, bumper-to-bumper traffic density
- WEATHER CONDITIONS
- Heavy rain, fog, sun glare, all cause low visibility
Remember, the speed limit is the maximum speed allowed, it’s not the goal.
If you’re a bike rider, think carefully about the roads and the speed limits that are safe for you to ride on.
Just like driving any vehicle, you can put yourself and other road users in danger if you ignore these factors.