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Roadcraft illustrations

Chapter 5. Acceleration, using gears, braking and steering

Vehicle balance and tyre grip

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Tyre grip is not necessarily the same on each wheel. It varies with the size of the vehicle and the load on the wheel. This affects how the vehicle handles. Braking, steering and accelerating alter the distribution of the load between the wheels and so affect the vehicle’s balance.


Acceleration and vehicle balance

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Acceleration alters the distribution of weight between the wheels of the vehicle. When a vehicle accelerates, the weight is lifted from the front and pushed down on the back wheels. During deceleration the opposite happens. This alters the relative grip of the front and rear tyres.

During deceleration the rear tyres lose grip the front tyres gain grip. During acceleration the rear tyres gain grip the front tyres lose grip.


Chapter 6. Manoeuvring at slow speeds

Steering

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It is easier to manoeuvre a vehicle when reversing than when going forwards, because the steered wheels are at the back. This may seem counter-intuitive, but once you’ve achieved competence it is easier to be precise and to make steering movements at slow speed this way round. (As you increase speed in reverse, it becomes increasingly difficult to steer accurately.) This means that it is often easier to manage tight turns in reverse, provided you have a good enough view to do so. There’s a trade-off between vision and manoeuvrability, particularly for larger vehicles like vans and trucks.

Remember to allow for overhangs. Even a small vehicle will have some overhang from the wheels, and in a tight space it will move differently when steering. The tighter the steering lock, the more pronounced this is.


Chapter 13. Emergency Response

Responding on multi-lane roads

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On multi-lane roads equipped with central reservations, such as dual carriageways and motorways, your positioning will vary according to the volume and speed of vehicles ahead. In very congested conditions where vehicles are either stationary or travelling at low speed, it is best practice for police drivers to straddle lane markings to allow the traffic ahead to spread left and right. This is often referred to as ‘parting of the waves’.

Be aware that some of the drivers ahead may not react as expected. Your approach speed must enable you to react to any vehicle crossing your path.


Vehicles responding in convoy

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Two or more vehicles travelling together in response mode is more hazardous than a single vehicle. The public sometimes only react to the lead vehicle, and once it has passed may resume their journey into the path of the second vehicle.

Be aware that other drivers may not anticipate the presence of a second emergency vehicle.

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