I've been told 'coasting' in a car is illegal and dangerous. Is this correct? Surely it saves petrol.......

Answer 1

Coasting in itself is not an offence in the UK, furthermore on a modern car it actually uses MORE petrol than keeping the gear engaged with the throttle completely shut. Here's why... When the car is moving and you take your foot off the gas, a device engages in the electronics where only the tiniest amount of fuel is injected into the engine, to to keep the combustion process going. When the car's in neutral, either because your foot's on the clutch or you've taken it out of gear, there has to be enough fuel going into the engine for it to 'idle' at 700-800rpm, whilst also driving the power steering, alternator, aircon pump etc. If the car is rolling and in gear, all that is taken care of by the momentum of the car, which is why it does slow down eventually.

Answer 2

I'd just like to wade in here...

If you have a crash whereby you are injured seriously, chances are you are not going to be thinking about putting the car in gear, that's how the law enforces it, after the crash when your car is on it's roof in neutral and they ask the question why.

Secondly, engine braking is the reason you should keep your car in gear in terms of control, you tend to use the same foot to break as you accelerate with, so the engine is starved of fuel and additional braking power comes into force this does not occur in neutral and maybe needed if going down a hill where a car was to suddenly pull out in front of you.

I have done this once or twice in the past, thinking the same, when I realized the errors of my ways I stopped.

Answer 3

It is "Illegal" in UK. This dates from the days when cars had only a single braking system of questionable efficiency (Pre ~1925~), so It was essential to keep the gears engaged to ensure some control of speed on descents. It comes under "not having proper control of the vehicle", so on a modern vehicle it is perhaps an arguable point. It's unlikely to be an issue unless you have a smash. Most modern cars have a complete fuel shut-off when on the over-run anyway so you won't save much by coasting against closed throttle in top gear.

Answer 4

Hi, While costing in neutral, although your foot is of the accelerator, the engine continues to run at its minimum speed (idle rpm) where a predetermined amount of fuel is constanty supplied by the fuel injection system. The concenr regarding safety is real - when you are coasting in neutral the engine is disonnected from the wheels and if you need to come to a stop you are toally dependand on the brakes. At slower speeds this is not so much of a problem - but if you are costing at lets say 50 miles - you will find it hard to bring the car to a stop in a hurry, as opposed to being engaged in a gear and trying to decelerate from the same speed to a complete stop. You also increase the chances of locking up your wheels when you brake hard in neutral, unless you vehicle has abs. Engine braking - this is when the engine is running slower than the wheels ( typically happens when you shift to a lower gear and suddenly release the clutch in a stick shift OR while you shift to a lower gear going downhill & release the clutch without stepping on the accelerator - you find the car slowing down although you have not hit the brakes) - this is engine braking.

Answer 5

the fuel saved by coasting is just not worth the bother. Also many modern engines have a sensor which cuts off the fuel to the engine when you are slowing down with your foot off the gas pedal, so no fuel is used. But if you are coasting then the engine goes into 'tick over' mode and therefore uses some fuel.

Answer 6

You are required by law to be in control of the vehicle at all times. "Coasting" means that the engine is disengaged from the road wheels and the car will become unwieldy and difficult to nigh on impossible to keep under control at speed.

The proper way is to have the engine drive the car, and not the car drive the engine. The torque of the engine is sufficient to slow the car without substantial input from the driver, except to steer the vehicle.

My grandfather did this often in a vain attempt to save petrol and ended up only putting the family's lives at risk.

Far too many people do not take driving seriously and that is when accidents are caused. I emphasise that accidents do not merely 'happen' - they are always caused.

A momentary lapse in concentration, at speed, while the vehicle is coasting, may not lead directly to a fatal accident where the driver dies, but may lead to the deaths of other road users as the 'coasting' driver struggles to regain control of the vehicle.

Answer 7

It does indeed save fuel...

But in this day and age, with the cost of fuel where it is, and all the concerns about the environment, pretty much every safe and legal method of saving fuel has already been discussed on TV, the newspapers, and magazines. Ever seen anybody do an article about the fuel saving benefits of coasting?

I haven't, but I have seen articles about how dangerous coasting can be, because it does save fuel, and people used to do it a lot back in the seventies.

Answer 8

Like Peter G says, it is still illegal in the UK. And actually it uses more fuel than if you let the throttle shut and go downhill, f'rinstance, on a trailing throttle. In neutral, the engine uses fuel to keep idling, whereas with modern fuel injection systems no fuel is used at all while the engine is being driven by the car.

Answer 9

In those places where it's illegal - I'd sure like to know how anyone could get pulled over and ticketed for it. There's no way a cop, from outside of your vehicle, can tell if your shift lever is in neutral or whether or not you're depressing the clutch.

Sounds like a stupid law, mainly because it could not possibly be enforced.

Answer 10

everyone talks about going downhill not saving fuel, but what about a long road where if you coast, you can gradually slow over half a mile whereas if the engine were engaged the car would come to a halt. This surely *would* save fuel?