Factors Affecting Stopping Distance

• Factors Affecting Stopping Distance

  • The stopping distance is the distance travelled by a vehicle from the moment the driver acknowledges the need to stop to the vehicle coming to a complete stop
  • It is determined by a combination of the braking distance and the thinking distance
• Braking Distance

  • The braking distance is defined as:The distance travelled by a car under the braking force - i.e. whilst it is slowing down
  • The main factor affecting the braking distance of a car is its speed
  • The greater the speed, the greater the braking distance will be
• Braking Distance

  • There are additional factors which affect the braking distance, such as:
  • Vehicle condition - e.g. worn tyres or poor brakes
  • Road condition - wet or icy roads make it harder to decelerate
  • Vehicle mass - a heavy vehicle, such as a lorry, takes longer to stop
  • The smoother the road conditions, for example when they are wet and icy, the less friction there is between the tyres and the road surface so there would be a greater braking distance
• Braking Distance

  • The braking distance is the ratio of the kinetic energy of the car and the braking force
  • This is because the work done in bringing a car to rest is the transfer of all its kinetic energy into other forms (thermal, sound)
  • The kinetic energy is equal to

  KE = ½mv2

  • This means the braking distance is proportional to the velocity squared
  • If the velocity doubles, the braking distance increases by (2)2 , 4 times!
• equation of braking distance

  
• Thinking Distance

  • The thinking distance is defined as:The distance travelled by a car from when a driver realises they need to brake to when they apply the brakes
  • The reaction distance is equal to:

  Reaction Distance = Speed of the car × Driver’s reaction time
• Thinking Distance

  • The main factor that affects the thinking distance is the car’s speed, however additional factors can affect the thinking distance
  • It is increased by:
  • Tiredness
  • Distractions (e.g. using a mobile phone)
  • Intoxication (i.e. consumption of alcohol or drugs)
  • Since these factors can affect the driver's reaction time, they directly affect the thinking distance
• Dangers of Large Decelerations

  • A large declaration can be dangerous for a number of different reasons
  • For any object to decelerate, a force is required and for heavy objects, large decelerations will require large forces
  • This is true according to Newton’s Second Law:

  F = ma

  • Where:
  • F = force in newtons (N)
  • m = mass in kilograms (kg)
  • a = acceleration in metres per second squares (m/s2)
• Loss of Control and Injury

  • When a vehicle undergoes a deceleration then the driver and passengers also experience a deceleration
  • This can cause injuries such as whiplash is a neck injury caused when a persons head moves suddenly, relative to their body
  • It is also more difficult to control a vehicle that is decelerating
  • Losing control can cause a collision