Controlling speed

When assessing risk speed is one of the most critical issues. Risk is linked to speed, surprise and space. The chances of something negative happening are higher if you are surprised by something or if you do not have space around your vehicle or if you are travelling at higher speeds.

You can reduced the number of times you are surprised through good hazard awareness, you can choose to keep your distance from other objects through good positioning and you can monitor your speed closely to make sure you are driving at an appropriate speed. 

This is one of your key tasks: to have excellent control over your speed. Let’s look at the different ways you control the speed of your vehicle.

the accelerator

Evidently a key method of controlling your speed is to use the accelerator. When you are in gear the harder you press the accelerator the faster the car will go. When you come off the accelerator the car will begin to slow down. 

The only way (besides the effect of gravity when travelling down hill) to make your car go faster is to press the accelerator. You cannot use the gears to make you go faster (though less pressure on the pedal will be needed in different gears to get the same level of acceleration). So if you want to increase you speed by 10mph this will be done in a shorter amount of time if you use 1st gear compared to 6th gear but either way you will need to apply pressure to the accelerator pedal.

When it comes to slowing down: in many situations simply coming off the accelerator is enough initially. For example, if I see a roundabout sign ahead then after having checked my mirrors and determining it is safe to do so I simply come off the accelerator and let the car begin to slow whilst I collect information about the roundabout and assess what I need to do to navigate it safely. The slower my speed at the start the less likely I am to need to brake, conversely if I am traveling at 70mph, coming off the accelerator will drop my speed (perhaps by 5-10mph) but after that point it will take a very long time for it to drop significantly. I am therefore going to need to use the brakes.

    the brake

    Obviously the brakes will slow the car down and if you slow a vehicle down enough it will be brought to a stop. The more firmly you press the brake pedal the more quickly the car will stop. Modern day brakes are very effective and you will often need only a light touch on the brakes to effect a change of speed. As always though whatever vehicle you drive you will need to do what is necessary to control it – so if that means pressing the brakes hard then do!

    It is really helpful for the road users behind you if they have some warning that you are slowing down or stopping, so slowing down gradually and giving people time to see your brake lights is really helpful. (It’s also why it is so important that your brake lights work).

    use of gears

    The gears can be used to slow the car down because they control the power ratio (torque) coming from the engine. This is not the most effective way of slowing the car down and the brakes are the preferred method (they are cheaper to replace!).

    Gears will also have an affect on how the car handles when you come off the brake pedal. When you come off the brakes the momentum will continue to take the car forward and the gear that you are in will have an effect on the speed you settle at. For example, in my car if you brake to below 8mph whilst in 2nd gear and then release the brake the car will pick up speed slightly and settle at about 11mph. If you brake to below 8 mph and change into 1st gear then release the brake the car will stay at that speed.

    momentum

    Momentum is the measurement of an object in motion -every thing that moves has momentum. How much momentum some thing has depends on it’s size and how fast it is travelling. Therefore a large truck travelling at 10 mph has more momentum than a  small car travelling at 10 mph. The more momentum some thing has the greater the force required to stop it. 

    This has two important applications in driving:

    1. Bigger, heavier or faster vehicles take a greater force to stop and that often translates into taking longer to stop, i.e. the brakes need to be acting on the wheels for longer.
    2. If you hit some thing or someone then the speed you are travelling at and the size of your vehicle will largely determine the amount of damage you cause.

    Therefore consider carefully what speed you choose to drive at and understand that the weight of your vehicle will affect the stopping power you have. This is particularly important when you swap between vehicles or have more passengers than normal.