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BP Ultimate Green Driving Test: Just how far can a litre of gas go?

By Phil Boucher

Changing the way you handle your car can greatly reduce its impact on the planet

It's not how I normally drive up a hill – four wheels spinning wildly and gradually sliding backwards. Plus, I was supposed to use the accelerator as sparingly as possible, yet was thrashing the engine towards the breaker's yard. The smirks from the BP technicians were also slightly off-putting as I fumbled with the clutch and provoked a series of angry yelps from the gearbox. All things considered, my first attempt at green driving wasn't going that well.

Worse still, the aim of the BP Ultimate Green Driving Test was child-pleasingly simple: I had to drive a Ford S-Max around the Millbrook Proving Ground in Bedfordshire and do my best to complete its eight-mile course on a single litre of petrol. Meanwhile, a team of BP engineers would measure my every move through an engine-linked computer to reveal exactly how efficient my use of fuel was and, by extension, how much CO2 and other harmful emissions I pump into the atmosphere whenever I put a key in the ignition.

Yet I was not at Millbrook to feel guilty. The whole philosophy behind green driving is that anyone can reduce their emissions if they adopt a few simple techniques, such as using the momentum of the car to propel you forward and minimising the amount of accelerating and braking. Other more routine measures such as maintaining the correct tyre pressure, reducing unnecessary weight in the car and shutting your sunroof or windows are also known to help.

The idea is simply to minimise the amount of work your engine has to do; the basic principle being that the more strain it's put under, the more fuel it burns. Which, given there are some 28 million cars on Britain's roads, producing 19.4 million tons of carbon – or 13 per cent of total carbon emissions in the UK – is a remarkably simple way to help the environment.

"If one person adopts green driving techniques it's not going to halt the rise in sea levels," explains Bob Saner, independent consultant at the Energy Saving Trust. "But if everybody adopts the techniques you may see vehicle CO2 emissions drop by around 10 per cent. It's not a total solution but the beauty is that it's a no-cost solution and can be done immediately."

Yet back on the track it was proving fiendishly difficult to put into practice. Normally, Millbrook is used to test cars under quantifiable road conditions – it's thanks to the proving ground that we have statistics for things such as durability, handling and miles per gallon – so its eight miles of tarmac are designed to replicate every type of driving condition, with A-roads, country lanes, motorways and the stop and start of big city traffic all coming on top of one another.

Out in the real world I generally handle all of these environments with ease, yet I found myself brain-achingly confused the moment I set tyre on the first "A-road" section. Having built up a bit of speed I tried to let the car's momentum gracefully carry me around a corner, only to come to a halt at the midway point and have to attempt some weird version of a hill start on a billiard-table-flat road. Moments later I repeated the feat on a proper hill, coming to a complete halt a couple of yards from the summit and painfully crawling the last few inches in first gear. I then careered off the tarmac as I attempted to slide down the back of the hill in fifth. For the first time since my teenage driving lessons, the questions of where to brake, what gear to select and how hard to accelerate completely frazzled my mind. I had even forgotten to shut my window.

Yet the worst was still to come. Slap bang in the middle of the course I came face to face with the "truck stops": a pair of ski-jump-sized slabs of concrete set at 25 and 20 degrees to the horizontal, and designed to test clutches to breaking point. Millbrook technician Anthony Sale later revealed the key to eco-friendly hill climbing is simply to "keep the car in first gear and gently bring it up the slope between 2,000 and 2,500 revs". I opted to start in first and change into second once the car was rolling, thinking it would burn less fuel. Seconds later, I found myself sliding backwards and had to gun the engine for all it was worth to recover.

After a lot of wailing from under the bonnet, I eventually made it to the top – only to hear the fuel buzzer sound on the dashboard. I'd spent my entire petrol quota within the first three miles of the course and failed about as dismally as it's possible to do.

Back at the exhaust emissions laboratory I braced for the worst and wasn't disappointed. "You were on and off the throttle quite a lot, which really wastes fuel," explained Sale. "There was also a lot of coasting with your foot on the clutch and the gear in neutral. Plus, you didn't really use the hills or the momentum of the vehicle to your advantage in any way at all."

According to Millbrook, a perfect run on its test course in the S-Max uses 34 miles per gallon and emits 191 grams of CO2 per kilometre. I managed to clock up a paltry 22mpg while pumping out a massive 294 grams of CO2. That translates to 54 per cent more fuel and, when spread over an average of 10,000 miles per year, a whopping 35 per cent extra CO2 in the atmosphere. That's around an extra ton-and-a-half a year. BP estimates that I could save myself a minimum of £700 a year simply by driving in a fuel-efficient way.

More importantly, my results were actually fairly typical. The BP Ultimate test has discovered that the vast majority of drivers cost themselves between £500 and £1,500 a year while unnecessarily pumping out thousands of tons of needless CO2.

"Simple things such as making sure your tyres are pumped up, that you're not carrying unnecessary weight and you accelerate and brake gently really do make a difference," explains Tony Bosworth, senior transport campaigner at Friends of the Earth. "Plus, it has a double benefit: you're cutting down on pollution and helping your wallet, too."

From 2008, eco-driving is set to become a standard feature of the UK driving test. As for the rest of us: we'll just have to accept that although it's difficult to drive in a green way, this is one case where old gas guzzlers really do have to learn some new tricks – no matter how embarrassing it may be.

Top 10 tips for greener motoring

* Check your tyre pressures

Under-inflated tyres increase the rolling resistance between the car and the road, forcing the engine to work much harder.

* Maintain your car

Poorly maintained cars suffer from poor oil performance and under-performing emissions control systems.

* Improve your aerodynamics

Open windows and sunroofs, plus external fittings such as roof boxes and bike racks increase the aerodynamic drag of your car and force the engine to work harder.

* Switch off air conditioning

Switch on the air conditioning and your engine immediately has to work harder. It's best to run the air conditioning for a few minutes then switch over to your blowers.

* Avoid stop-start

Avoid driving during congested periods of the day as constantly starting and stopping the vehicle causes the engine to work harder than ever – particularly true if you're carrying a heavy load.

* Look ahead

Keep a close eye on the traffic ahead of you so you can lift off the accelerator and gently slow down. Modern cars will turn off the fuel injectors if you coast in gear, meaning you'll burn no fuel at all.

* Avoid hard acceleration

Sudden acceleration forces the engine to consume extra fuel. To save fuel, accelerate steadily.

* Look at your rev counter

To get the most out of a petrol-driven car you should change gear when the revs are below 2,500rpm and try to keep them within 1,500 and 2,500rpm.

* Avoid short journeys

On short journeys when the engine is cold a car uses more fuel because some is used to heat the engine itself. The catalytic converter in the exhaust, which reduces harmful emissions, is also less efficient when used cold.

* Use better fuels

High-quality fuels contain cleaning agents that reduce emissions and ensure carbon deposits don't block the flow of fuel inside an engine. This maximises fuel efficiency and can reduce unburnt hydrocarbon and carbon monoxide emissions by as much as 30 per cent

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