Section 4.4 Why speed kills cyclists

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Cyclists face much greater risks riding on roads than when riding on grade separated bike paths. Collisions with a motor vehicle may be fatal. What makes a motor vehicle so deadly?

Vulnerable Road Users

Vulnerable road users are typically cyclists and pedestrians. People are soft but motor vehicles are not. When the two meet, it can be fatal. The problem of speed is discussed in Austroads Integrating Safe System with Movement and Place for Vulnerable Road Users.[1]

[1] B. Corben, Integrating Safe System with Movement and Place for Vulnerable Road Users. Sydney, Austroad, 2020, https://austroads.com.au/publications/road-safety/ap-r611-20, 14, [accessed 7th July 2021)

Fatalities depend on vehicle speed

The relationship between the speed and energy of the motor vehicle is unfortunate. The cyclist will likely die in a collision with a car travelling at 50 km/h. The good news: reduce the speed of the car to 30 km/h and the cyclist will almost certainly survive, but injuries are still very likely. Cycling on bike paths on the verge and away from the road are safer than riding on the road.

Relationship between collision speed and the probability of a fatality. Source: Integrating Safe System with Movement and Place for Vulnerable Road Users (Austroads,2020)
Figure 4-5 Relationship between collision speed and the probability of a fatality. Source: Integrating Safe System with Movement and Place for Vulnerable Road Users (Austroads,2020)

The problem of energy

Motor vehicles at speed carry an enormous amount of energy that can shred two cars when they collide.

Double the speed of the motor vehicle and the energy increases four times (figure 4-6). Small increases in speed result in large increases in energy. The opposite is also true. Small reductions in road speed greatly reduce the energy and with it any fatalities. Reducing motor vehicle speed is the most effective and inexpensive measure to improve road safety.

Figure 4-6 The energy of the motor vehicle increases rapidly with increases in speed.

The problem of braking

Stopping distances greatly increase with speed due to the energy relationship. The situation is worsened by human reaction times. Our brain takes relatively long to react to danger. Nothing we can do will shorten it. Distractions such as phones make it longer still. Even with the best intentions, our concentration will lapse and be slowed by fatigue.

In half of all fatal bike cycle collisions, the driver never manages to brake.[1] This is why decreasing road speed limits make such a big difference.

The stopping distances of typical passenger cars for a range of initial travel speeds are shown below. A car travelling 50 km/h will take 30 m to stop and will have moved 20 m forward without any speed reduction before the driver can react and brake.

[1] B. Corben, Integrating Safe System with Movement and Place for Vulnerable Road Users. Sydney, Austroad, 2020, https://austroads.com.au/publications/road-safety/ap-r611-20, 14, [accessed 7th July 2021)

Stopping distances of typical passenger cars for a range of initial travel speeds (calculations assume a coefficient of friction of 0.70 and a driver perception-reaction time of 1.2 seconds). Source: Integrating Safe System with Movement and Place for Vulnerable Road Users (Austroads,2020)
Figure 4-7 Stopping distances of typical passenger cars for a range of initial travel speeds (calculations assume a coefficient of friction of 0.70 and a driver perception-reaction time of 1.2 seconds). Source: Integrating Safe System with Movement and Place for Vulnerable Road Users (Austroads,2020)

Making things better ๐Ÿ™‚

So, what can we cyclists do to help change our car and speed loving culture? Here are a few ideas:

  • ๐Ÿ˜Š Slow down when you pass a cyclist to set a good example. Emotions are contagious!
  • ๐Ÿ˜Š Educate your family and friends about the risk of them driving too fast around cyclists.
  • ๐Ÿ˜Š Use your lights and wear high vis bike clothing to make it easier for drivers to spot you.

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