An average car, sat idling, can produce exhaust emissions to fill 150 balloons. That's a lot of balloons to imagine puffing away out of the cars idling outside a school for a pickup, say. Other tests have found (pdf) that for any time over 10s fuel use and emissions are always greater when idling than turning off the engine and restarting. Spread the word.

Of course, if you have an electric car this won't apply.

I did draw 150 balloons, but a few of them didn't fit on the page.

Idling

Jevon's paradox is that improvements in fuel efficiency tend to increase fuel use, not decrease it as you might expect.

In 1865, a chap named William Stanley Jevons noted that while there had been a number of improvements in coal efficiency in steam engines and the like, the effect was to increase consumption instead of reduce it. This observation became known as Jevon's paradox.

While it’s not a surefire outcome, there are plenty of parallels like more efficient batteries leading to more overall battery use, washing machines leading to doing more washes rather than less time spent washing, or the ability to recycle some plastics leading to more overall plastic consumption.

In her book More Work for Mother, Ruth Cowan addresses the ironies of household technology and how improvements in the efficiency of household devices often led to more work, not less.

This is sometimes known as the rebound effect.

Jevon’s Paradox

Marchetti's constant is the idea that people across history budget, on average, about an hour a day for travelling. Originally observed by Yacov Zahavi, it came from the observation that even as our means of transport sped up, instead of travelling less each day, we would just travel further. As in the sketch, this leads to a conclusion that the size of our cities increases partly according to how efficiently we can travel in and out—they generally increase to a size that maintains about an hour round-trip journey.

Cesare Marchetti observed that Greek villages and ancient walking cities, for example, as marked by ancient city walls, tend to share a radius of about 2.5km. Walking at a typical 5km/hr makes a one-hour round-trip journey. He also pointed out that: “Even people in prison for a life sentence, having nothing to do and nowhere to go, walk around for one hour a day, in the open.”

Unfortunately, if you live in London, the average round-trip seems to be an exception of 1h30.

This is also known as the constant travel time budget hypothesis.

Also see isochrones. It might be interesting to look at these according to transport method…

Image adapted from: Marchetti, C., 1994: Anthropological Invariants in Travel Behavior, Technological Forecasting and Social Change , 47 :75–88, Internal Publication, International Institute for Applied Systems Analysis.

Marchetti’s constant

This is surely at least part of the reason that “software is eating the world.”

But I’m sure coffee will stick around for a bit too.

Rival and non-rival goods

I think it would be interesting if we could see the real shape of your favourite crossing marked on the road. It’d probably help more people cross and traffic get stopped less. And, hopefully, no casualties.

Our senses are built to take in information at human pace

The real shape of a crossing

The piston is an amazingly simple, ridiculously useful and successful mechanism that, together with a connecting rod and crankshaft, converts linear motion to rotational motion.

This simple system is basically what allows us to take a force produced by, say, steam or an explosion and make a wheel turn. Stick a few of these together and time the rotation of each correctly, carefully controlling the explosions and the exhaust, and you have an internal combustion engine that powers and moves our cars.

There are a lot of amazing things to me about it, but I am still impressed with how effectively it takes something moving back and forth and makes something spin around and vice versa.

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Category: cars