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Comment by Lramseyer | Hacker News Reader

One thing that's very important to keep in mind when looking at air travel emissions is how fuel efficient planes actually are. The math works out to around 100 miles per gallon per passenger. And at an underwhelming 2.5% of global emissions, I can't really put it in the category of "low hanging fruit."

That's not to say that we shouldn't invest in things like high speed rail, (because we absolutely will see quality of life improvements for North America) but I'm more excited about improvements in vehicle transportation and energy production.

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Yes, while 100 mpg per passenger is roughly 2x the best hybrid car, the presence of air travel as an option, especially in a business context allows individuals to accrue many orders of magnitude _more miles_.

MPG per passenger is the wrong unit.

Gallons per person per hour of active transport seems like a better unit to measure.

For example, say your non-hybrid car gets 30 mpg, and you average 30 miles per hour between city/highway, you're at 1 gallon per hour per passenger, assuming 1 person per car.

For air travel averaging out at 500 mph, the 100 miles per gallon per passenger equates to 5 gallons per hour per passenger.

So you would need to pack a plane with 5x the number of people that the 100 mpg number was measured at to even COME CLOSE to hitting the miles/passenger-hour of a non-hybrid car driven by a single driver.

That's a crowded plane.

Passenger-hour is not an appropriate metric here. passenger-miles is.

But I should point out here that electric cars usually get 100mpge or better. And it's already feasible to do road trips in a Tesla. I'll be doing a (short) road trip with my first-gen Leaf.

For domestic trips, we can replace air travel with regional electric buses in the near term and electric airplanes in the mid-term. In the far-term, we can do even long-haul air travel using lithium-air batteries or very high performance lithium/sulfur or lithium metal anode batteries and extremely efficient airframes and multiple hops. That'd be faster and cheaper (at least in the US with high infrastructure costs) than high speed rail.

> electric cars usually get 100mpge or better

Right, and the mpge metric is flawed, because it assumes a (typically bad) energy mix.

5km driven in the UK is equivalent to 100km driven in Sweden.

The former sits at an average of approx. 300gCO2e/kWh. The latter at 15gCO2e/kWh.

With electric cars, the ultimate situation is that all of the carbon cost is in the production of the car/roads and maintenance thereof. Which is another issue that can be targeted and mitigated.

By contrast the only ultimate hope for a combustion powered plane or car is carbon capture.

The 'MPGe' of an electric car in a country with 90%+ renewable energy is like, 1000 or something daft like that.

That's a very odd measure. That would put driving the car at 15mph getting 20mpg as better than 30mph getting 30mpg.

The manual choice of what is low-hanging fruit is a path to failure. Instead, we should just tax the emission of the dangerous substance. So today, we'll do CO2. After a while, we'll include CH4. Then with a total cap on carbon, we allow the market to trade the right to carbon.

This will allow money to flow to the right places.

If your implementation means that a person in the third world cannot afford a fire to cook meals but a person in the first world can afford a huge fire pit for cooking marshmallows I would say you are well on your way to creating a dystopia. But hey perhaps they could pay for their emissions using those digital microloans!

Can't do it. Flammable material is readily available so they won't play the game if it means they'll starve (which is how I'd do it). I can't impose that on these people and it is an outcome that is absurd so I'm sure we can make something work here.

The math works out to around 100 miles per gallon per passenger.

That assumes maximum passenger load, I assume.

At maximum passenger load, my car gets 170 miles per gallon per passenger.

A giant, gas-guzzling Chevy Suburban gets 198 miles per gallon per passenger.

I don't think "per gallon per passenger" is a useful measure.

your car is full probably 5% of a time, airlines have profits from full planes, you don't.

"per gallon per passenger" is a useful measure for planes.

If you’re running an airline, yes that’s the relevant metric. If you’re comparing an urban elite with a poor bloke with his truck, no.

Mr. Loves-his-truck drives, at the insane most, 20 000 miles a year. That’s a round trip Thai vacation.

I think it is.

Freight is typically measured in cargo-ton-miles per gallon. I can't think of a reason to measure airline travel in other than passenger-miles per gallon. (You have to do it "as flown" and "as driven" for the comparison to be meaningful, but it's pretty rare for me to see anything under a 90% full flight lately with the economy booming.)

Just feel like pointing out that airplanes are flown maximum passenger load or close to it as much as possible whereas you can see just by looking around in traffic that passenger cars are mainly driven with one person inside.

They’re also flown very far away.

That is the value with something close to capacity, but most importantly assuming worse case for weight. And weight has a bigger effect on the consumption on a plane than on a car. So if your plane has less passengers, the MPG of the plane increases, though the MPG/passenger decreases. And it is also mainly for cruise - the longer the travel, the better the efficiency. Taking off and climbing is not that efficient so short haul trip are quite bad.

To me the point is that an airplane MPG/passenger is of the same magnitude as the MPG/passenger for an individual car. What is bad is not necessarily the plane itself, but the fact we do very long distance trips. Trains and buses can be more efficient, carbone-wise, but requires a traffic big enough to offset the carbone cost of the infrastructure needed.

Big deal; it’s a bus with wings. My seven seat SUV gets 210 passenger mpg.

But if I vacation with my SUV, I’ll go 600 mi. away as an absolute maximum or about a days worth of driving. That’s 7.5 gal per person for my family of four

If I take a plane, I’ll stick to a 24 hr travel limit. Which will get me a third the way across the world, or 83 gal for every member of my family.

In scenario 1, I’m a redneck with a family in Virginia Beach.

In scenario 2 I’m an enlightened cosmopolitan in Machu Pichu

There’s a simple metric: how much you spend on petrol versus paying for flights.

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