> Actually, you laugh, but I did see a report about a car that has a giant 
> motor inside it that drives the wheels at low speeds,

A useful tip that (apparently) not many people know, is that if you've 
broken down in a dangerous location you can use the starter motor to move 
along at slow speeds in *any* car (ok maybe not in those american 
automatics).  Just put it in 1st gear and try to start the engine - it will 
allow you to move the car to a safer location (assuming you don't also have 
a flat battery!).

> The big advantage being that waiting at traffic lights uses no fuel.

My car does that already - as soon as you are stationary, in neutral, and 
let go of the clutch pedal, the engine stops.  And then as soon as you touch 
the clutch pedal it restarts.  Apparently meant to save a few % of fuel when 
driving in cities.

> [Actually, having computed that my car uses 10^(-6) L of fuel per minute 
> even when it's flying down the road at 75 MPH,

Wow! What car do you have with such great fuel economy? ;-)

> I wonder just how much fuel it can possibly be wasting on tickover?

I had a Ford once that showed the fuel economy in realtime as you were 
driving, but if you were stopped it switched to litres per hour, was 
something like 1.5 litres per hour IIRC when stationary.  I rememeber 
figuring out I could leave it running for a day or so until it used up a 
full tank.

> And also, doesn't repeatedly starting up a petrol engine waste fuel 
> anyway?]

Depends how warm the engine is and how often you restart it.  For a fully 
warm engine I think that if you're going to let it idle for more than a few 
seconds it's better to switch it off and restart.

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