How many miles of train tracks exist in the world?
Radius of Earth = ~3,000 miles
Surface area of earth = 4 x pi x r^2 = 1.13 × 10^8 = ~10^8
25% of the earth is land
10% of the land “needs” tracks
.1% of that land actually is tracks
10^8 x .25 x .1 x .001 = 2,500 miles
This feels obviously wrong, so let’s buff the numbers:
Radius = 5,000 miles, 30% of the surface is land, 25% “needs” track, .5% of the land is tracks
3.14 x 10^8 x .35 x .2 x .005 = ~110,000 miles
Let’s round that off to 100,000 miles.
Edit: Thanks to the comment from @philh, I see that I calculated square miles rather than linear miles. Assuming the width of a track is 1/1000 of a mile:
2500 x 1000 = ~2.5 million miles
This feels reasonable, so if I had performed that step, I would not have done a second round of estimation.
How many metric tons of air freight cargo shipped globally in 2009, and in 2019 (either by commercial airlines or specialized freight companies)?
How much stuff did I order? Everything I use was shipped from somewhere.
Amount of stuff I ordered last year: 200 pounds
That feels low when I think about heavy food and drink containers, so let’s bump to 1,000 pounds
My share of infrastructure “stuff” feels smaller than that, so no modifier.
Most of the world uses less stuff than I do (age, affluence), so nudge it down to 700 pounds.
A ton is 2,000 pounds
Population of the world: 7 billion
7 billion * 700 / 2,000 = ~2.5 billion
Let’s assume 2% growth per year
1.02^10 = 1.22
2.5 billion / 1.22 = ~2 billion
2019: 2.5 billion tons
2009: 2 billion tons
After reading the answers from others, I’ve realized that I assumed all freight was by air. If I had considered that, I would apply a discount factor, revising significantly downward. Keeping my original answer in the spirit of the exercise.
It looks like your calculations are giving you square miles of track. If a track is 1/1000 of a mile wide (1.6 meters? sure, close enough, judging by the height of a damsel in distress), you’d have 2.5 million linear miles from your first estimate, and 100 million linear miles from your second.
How many miles of train tracks exist in the world?
Radius of Earth = ~3,000 miles
Surface area of earth = 4 x pi x r^2 = 1.13 × 10^8 = ~10^8
25% of the earth is land
10% of the land “needs” tracks
.1% of that land actually is tracks
10^8 x .25 x .1 x .001 = 2,500 miles
This feels obviously wrong, so let’s buff the numbers:
Radius = 5,000 miles, 30% of the surface is land, 25% “needs” track, .5% of the land is tracks
3.14 x 10^8 x .35 x .2 x .005 = ~110,000 miles
Let’s round that off to 100,000 miles.
Edit: Thanks to the comment from @philh, I see that I calculated square miles rather than linear miles. Assuming the width of a track is 1/1000 of a mile:
2500 x 1000 = ~2.5 million miles
This feels reasonable, so if I had performed that step, I would not have done a second round of estimation.
How many metric tons of air freight cargo shipped globally in 2009, and in 2019 (either by commercial airlines or specialized freight companies)?
How much stuff did I order? Everything I use was shipped from somewhere.
Amount of stuff I ordered last year: 200 pounds
That feels low when I think about heavy food and drink containers, so let’s bump to 1,000 pounds
My share of infrastructure “stuff” feels smaller than that, so no modifier.
Most of the world uses less stuff than I do (age, affluence), so nudge it down to 700 pounds.
A ton is 2,000 pounds
Population of the world: 7 billion
7 billion * 700 / 2,000 = ~2.5 billion
Let’s assume 2% growth per year
1.02^10 = 1.22
2.5 billion / 1.22 = ~2 billion
2019: 2.5 billion tons
2009: 2 billion tons
After reading the answers from others, I’ve realized that I assumed all freight was by air. If I had considered that, I would apply a discount factor, revising significantly downward. Keeping my original answer in the spirit of the exercise.
Comment on q1:
It looks like your calculations are giving you square miles of track. If a track is 1/1000 of a mile wide (1.6 meters? sure, close enough, judging by the height of a damsel in distress), you’d have 2.5 million linear miles from your first estimate, and 100 million linear miles from your second.
That’s a great catch, thanks! With that correction as a final step, I feel much better about my initial estimate!