Turn off car engine when idling more than 10 secs

[monotonehell]

Or catch a bus and save 100%

Bus fares are free?

Nitpicking works better when you read the posts...

But how often do you practice this in a day? Once or twice a day? And how much fuel can you save out of this?

To be perfectly honest, drive during off-peak hours and you'll save 20% more fuel than you do during peak hours, and also the way you accelerate from standstill will also have more apparent effects.

[Hooligan]

Fuel costs are just one part of the cost of running and maintaining a car.

[Edgar]

And those costs are more than worth it.

[Prince George]

This topic is really one of the reliable ways to start a nerd-fight. It's the automotive equivalent of when somebody in an office sends out mail urging everyone to turn off their computers & monitors when they leave to save electricity; you are almost guaranteed that within an hour someone will reply claiming that the surge of electricity when they are turned back on will increase the chances of damage the equipment sufficiently to make the savings a loss blah blah blah. You saw that kind of thread much more often in the days of CRT monitors, and before computers had reliable deep-sleep modes, but I guess the stop-your-engine-at-the-lights topic can still inflame the passions

Another good topic is "when I'm driving in the summer, should I run the air-con (stealing power from the engine) or open the windows (and increase your wind-resistance)?", or "don't compact-fluorescent lights (or solar panels) require more energy to manufacture than they will ever save?"

The simple fact is that although all these questions may have some objectively right and wrong answers, in the scheme of things they are probably totally irrelevent compared to the total amounts of resources that we consume every day. Turn off your engine or leave it running, CFLs or incandescents, recycle it or dump it, these are just marginal improvements at best. Until you're talking about an order-of-magnitude reduction, it just doesn't matter enough. This kind of thinking is a bit of a crutch, that maybe we can solve problems of growing population, diminishing resources, and spiralling energy costs by just having efficient cars and light bulbs and not changing anything about how we live. People can imagine and understand simple substitutions (driving a Prius instead of a Commodore) more easily than radical changes (travelling much, much less).

[Hooligan]

(driving a Prius instead of a Commodore)

I could even argue that a Prius does more enviromental damage than a Commodore

[Edgar]

(driving a Prius instead of a Commodore)

I could even argue that a Prius does more enviromental damage than a Commodore

Before you even go there, read where and what Prius batteries ends up before you start your arguement about how its batteries (if being disposed are highly contaminated) because no stock Pirus batteries are supposed to be disposed, unless by some irresponsible individual actions.

Toyota buys the batteries back from you (in the form of rebates) if they needs to be replaced, and these battries are recycable. They are not disposable batteries like the ones you use for your TV remote controls, and in fact, the average household who trashes their consumer batteries actually causes more environmental damages than of what comes from the Toyota Prius.

And for the fact, your average Commodores already does more environmental damages as soon as it starts. The amount of CO2 being emitted by the old-fashioned V6s and V8s are more than of the little 4-cylinder of the Prius. That's 230-250g/km (V6) and 343g/km (V8) versus 104g/km (old Prius) and 89g/km (new Prius).

[Omicron]

But let's not mention the environmental impact of discarding one already-built car for a new one that requires new factories or substantially re-tooled ones to produce it, or that imported Priuses (Prii?) require transportation by container ships as opposed to locally-built Commodores and Falcons, or the real-world fuel economy of commuter cars versus those used primarily on weekends, or all the Prius drivers making plane flights and buying their electricity from coal-fired powerplants, or the real-world economy of diesel-engined cars (or early-'90s economy hatchbacks, for that matter) with comparable fuel-consumption and a much-lower initial purchase price, or that the manufacturer has to fully subsidise your battery replacement before it becomes cost-effective, or that.....

Beware the one-size-fits-all answers from manufacturers firmly invested in one technology at the expense of all others.