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Economy driving: fun, illegal, or dangerous?
Posted Tuesday, October 25/05 in Driving efficiently
Economy driving equals boring, slow and safe, right?
Tell it to the judge!
What follows is a collection of techniques that are guaranteed to increase your efficiency - and may attract the attention of the local constabulary as well.
Some are fun, some are dangerous, some are illegal (some are all three), and I will neither confirm nor deny that I employ any of them. Also, the litiginous nature of our world dictates that I advise you not to try any of these.
So, on to the list. Dangerous, fun, illegal - or none of the above? You decide...
Drafting: At freeway speeds, more than half the fuel you burn goes towards overcoming aerodynamic drag. Reduce that resistance and guess what happens to your fuel consumption.
When the Honda Insight was launched, Car and Driver participated in a fuel economy challenge, and on the highway portion they averaged 121.7 mpg (US), with peaks of 150 mpg. This, in a car the EPA rated at 70 mpg highway. How did they do it? By driving the Insight through "a Hindenburg-size hole in the air." The role of the Hindenburg was played by a Ford Excursion, which they drafted for the 195 mile run.
(It's worth noting that the second place team finished at 83.4 mpg - without drafting - nicely illustrating the EPA-beating results that an expert driver can get.)
I actually know of fuel economy nerds who draft trucks to reduce fuel consumption. Personally, I prefer to see where I'm going.
Carving through the curves: Way back in 1991, a Canadian auto magazine called World of Wheels published an economy test of 2 identical cars over the same highway and city route to compare "normal" vs. "efficient" driving.
For the part of the test that included twisty country roads, the difference between the two techniques turned out to be less than they were expecting. How come?
Because the "normal" driver was also a race car driver, and he unintentionally used his racing skills to achieve better fuel economy than an untrained driver would have actually seen.
On twisty country roads, an "average" untrained driver will brake harder before turning in to a curve, drive more slowly through it, and then accelerate harder afterwards to get back up to speed again.
The race-trained driver, on the other hand, will steer a line that "straightens" the curve as much as possible, permitting a higher speed to be carried through it, with less braking before and less accelerating afterwards (assuming good visibility throughout). This technique conserves more momentum, and that's why it's more efficient.
Rolling through stop signs: According to Natural Resources Canada, up to 6 times more energy is needed to accelerate a vehicle from a complete stop than if the vehicle alredy has momentum of just a few kilometers per hour.
That's why yield signs or traffic circles (roundabouts) are a more efficient way of controlling intersections than stop signs or traffic lights.
Driving slower: Reducing highway/freeway speed is one of the easiest ways to see big improvements in fuel consumption.
A commonly used statistic: for every 1 km/h over 100 km/h, a vehicle will use 1% more fuel. E.G. 110 km/h uses 10% more fuel than 100 km/h.
On multi-lane freeway trips, depending on how far I'm traveling, I typically drive near or a little below the speed limit. But I also live in a mainly rural area, so I can get away with that in the light traffic on the stretch of freeway that passes through here.
When I get into heavier traffic, or if I'm on a 2-lane highway where folks can't easily pass me, I step on it. It's safer to go with the flow.
Related: accelerating gently is far more efficient than stomping on the loud pedal. However, I try not to "impose" my efficiency on other drivers. When merging from a stop into flowing traffic, I try to accelerate (as much as I can in a Firefly) so other drivers don't have to brake to accomodate me.
Overinflating tires: Economy nerds understand the importance of low rolling resistance on efficiency. One way to get low rolling resistance is to buy tires that are specifically designed for that purpose; low rolling resistance (LRR) tires are fitted on most hybrid and many electric vehicles.
Another way to reduce rolling resistance is to make sure tires are inflated to the manufacturer's maximum pressure rating. This appliese whether they are regular or LRR.
Rolling resistance can be decreased even further by exceeding the recommended pressure rating, and I know it's common practice among fuel economy nerds. However, ride quality gets worse as pressure goes up, as does traction and handling, particularly on bumpy or loose (gravel) or wet surfaces.
Switching off DRLs: it's a fact that daytime use of headlights both increases safety and fuel consumption.
The decrease in fuel economy - up to a few percent - depends on the type of system used, specifically on how much energy it requires.
Running with full illumination will use more energy than a reduced intensity DRL system. A low intensity DRL system typically only illuminates the headlights, whereas full illumination is the whole Christmas tree - headlights, front & side marker lights, tail lights and dashboard lights.
I run with low intensity DRL's on the Firefly, and when I'm driving vehicles that aren't DRL equipped, I manually switch on the headlights.
However, I have fitted an "off" switch to override my car's DRL's under specific circumstances: freeway driving (divided, controlled access), where their contribution to safety is negligible. (DRL's contribute most where other vehicles - or pedestrians - can cross or enter your path, e.g. at intersections, driveways, or in oncoming lanes of undivided highways.)
Staring at the MPG display: Many drivers will tell you that a sure-fire way to change your driving habits is to have fuel consumption information displayed on the dashboard while driving.
Toyota Prius owners - whose cars have a fairly large and detailed video screen for monitoring fuel consumption and operation of the hybrid system - will tell you that there is such a thing as too much information. It can be downright distracting.
I can't speak from experience... yet.
I just ordered a fuel-economy computer that I can plug into my car's ECU. Soon I too will be able to turn driving into a real-life video game. I'll be sure to keep you posted.
Update - Added Nov 19/05...
Shortcuts: Taking shortcuts around traffic lights / jams can reduce idling time or conserve momentum. But it may also be seen as "queue jumping" by the motorists you drive past, and depending on the route could be illegal in some jurisdictions. Be prepared to face the social consequences!
Local example: there's a particular traffic light in town where the majority of vehicles in the right hand lane (of 2 lanes in each direction) turns right. The sheer volume of right-turners has made it a de facto right turn lane, even though it's not actually marked as such.
The locals who are going straight through generally stick to the left lane. So even on a red light, cars to the right can continue to flow around the corner when cross traffic permits. But occasionally, someone who doesn't know the local driving culture stops at the red light ... in the right lane ... and DOESN'T turn! Imagine.
An attentive driver approaching the resulting traffic clot has the option of turning right into a driveway, about 10 car lengths back from the intersection, going through a tiny never-used parking lot, and on to a side street that ends up at the same road s/he was originally heading for.
Zig-zag. Save fuel. And face the glares of the drivers left behind.
darin AT metrompg D-O-T com, or here