Drive 25% More Miles on your Next Tank of Gas

Learn from Hypermilers for Fuel Economy and Save Gasoline (Petrol)

Jun 27, 2008

Follow these tips and improve gas mileage by a quarter by simply driving differently. No modification is needed to the car, just to the driver.

On an urban commute, most of the energy is consumed in accelerating the vehicle – changing its speed. This energy is then lost in braking, where it is lost, turned into heat in nearly all cars on the road today. By simply changing the way a car is driven, the losses can be reduced. In the example shown, the gas fuel efficiency of an eight-year old VW Golf which has more than 100,000 miles on the clock was improved from 33 mpg to 43 mpg over a seven-mile commute starting from cold.

Anticipate Conditions Ahead

The key to improving gas mileage is to reduce changes in speed. This does not just mean avoiding burning rubber when traffic lights turn green. Avoiding harsh acceleration is part of the story, but avoiding harsh braking is just as important. The easiest way to do this in urban driving is to leave a little more space to the vehicle in front. By looking ahead and anticipating obstacles that may mean a change in speed, the driver can drive at a more even speed, which is good for gas mileage.

Time the Arrival at Traffic Lights

Time spent stopped but with the engine running is fuel wasted. If lights are red ahead it is worth slowing down as soon as possible and approaching them slowly. If they change while the car is still moving, a lot of the energy used in accelerating the car from a standstill is saved, and no extra time is lost.

Shift to a Higher Gear

In a car with manual transmission, the optimum fuel efficiency usually occurs at lower revs than the optimal power. This often leads drivers to change to a higher gear later than they should for optimum fuel economy.

Drive Smoother - Drive Cheaper

By accelerating evenly and smoothly from the lights, the gas or petrol consumption is reduced, and this gives other drivers the opportunity to overtake if they wish. They may be standing at the next set of lights, but they have the right to drive in the style they wish. Reducing stop-go in urban traffic makes all the difference – some of this can be seen in the first part of the speed/distance graph attached to this article.

Motorway Driving

At higher speeds such as motorway or interstate driving, the main factor affecting fuel consumption is the speed of the vehicle. At higher speeds more energy is consumed in overcoming air resistance, and the energy-per-distance consumed rises as the square of the speed. Unfortunately this means that fuel efficiency is better at lower speeds like 50 mph rather than at 70 mph. However, such journeys tend to be longer so the time impact is worse – a 400 mile journey at 50mph takes eight hours whereas at 70mph it would take about two and a quarter hours less.

Taking Things Further

Experimental Verification

The same 7.3-mile commute was driven on two consecutive days. The weather and temperature were very similar – sunny with some high cloud and a wind speed below 5mph. The first mile of this journey consists of getting out of the suburbs and is a dense urban cycle of several junctions. The rest of the journey is in countryside, with the end of the journey involving some more junctions. The tank was about half full (in theory the reduced weight of fuel on the second standard run would reduce the improvement in mpg) and there was only the driver in the car.

The first journey was driven along the lines of this article by allowing the speed to fall approaching congested junctions until the junctions cleared, and accelerating smoothly, allowing the speed to fall as the modest hills were climbed and picking up speed on the downslopes. The fuel consumption was 43 mpg. The second journey was driven as usual, and the average fuel consumption was shown as 33 mpg.

The first journey took 20 minutes; the second took 17.25 minutes, resulting in an average speed of 21.9 mph and 25.4 mph respectively. Over a week (ten such journeys) the extra time taken would be about half an hour, and half a gallon of fuel would have been saved. In a month this would save two gallons, which would be a worthwhile saving.

Driving for economy on an urban commute can improve fuel consumption by about a quarter, without modifying the vehicle at all.

References

The copyright of the article Drive 25% More Miles on your Next Tank of Gas in Energy Conservation is owned by Richard Mudhar. Permission to republish Drive 25% More Miles on your Next Tank of Gas in print or online must be granted by the author in writing.