The study does not quote miles driven in their specific sample so I can’t talk to this or answer your question directly, and the national numbers don’t cover injuries. The numbers in the survey are also a bit vague about injuries, and include “possible injuries”, “injury with severity unknown”, and they are taken separately from incapacitating injury data. The data on injuries is objectively lower quality than the data on deaths, and anyway deaths was the focus of the original question, so I’d rather avoid getting sidetracked.

To respond to your question (admittedly not to answer directly), nationally there was indeed an increase in miles driven, an additional 59 billion miles in 2002 compared to 2001, and indeed there was an increase in deaths. I would also expect an increase in injuries as well.

Looking at this in isolation, you can say “oh so because of 9/11, people drove 59 billion more miles which resulted in more deaths and injuries”, but in my opinion real question if you want to understand the world better is “how many more miles would folks have driven in 2002 compared to 2001 in case 9/11 never happened”.

We obviously can’t know that, but we can look at data from other years. For example, from 1999 to 2000, the increase in miles driven was 56 billion, from 2000 to 2001, the increase was 50 billion and from 2002 to 2003 the increase was 34 billion, from 2003-2004 the increase was 75 billion.

Miles driven, injuries, deaths, are indeed all closely correlated. But so is population size, the price of oil, and hundreds of other factors. If your question is “did more people die on the roads in 2002 than in 2001”, the answer is yes. Again, I assume that the same is also true of injuries although I can’t support that with data.

That wasn’t OP’s assertion though, OP’s assertion was that closing down airspace does not lead to zero excess deaths. My argument is that the statistics do not support that conclusion, and that the additional deaths in 2002 cannot rigorously be shown even to be unusually high, let alone caused by 9/11.

> That wasn’t OP’s assertion though, OP’s assertion was that closing down airspace does not lead to zero excess deaths. My argument is that the statistics do not support that conclusion, and that the additional deaths in 2002 cannot rigorously be shown even to be unusually high, let alone caused by 9/11.

What we can show rigorously and directly is a tiny subset of what we know. If your standard for saying that event x caused deaths is that we have a statistically significant direct correlation between event x and excess deaths that year, you're going to find most things "don't cause deaths". Practically every dangerous food contaminant is dangerous on the basis of it causes an increase in x condition and x condition is known to be deadly, not because we can show directly that people died from eating x. Hell, even something like mass shootings probably aren't enough deaths to show up directly in death numbers for the year.

I think it's reasonable to say that something we reasonably believe causes deaths that would not have occurred otherwise causes excess deaths. If you actually think the causal chain breaks down - that 9/11 didn't actually lead to fewer people flying, or that actually didn't lead to more people driving, or that extra driving didn't actually lead to more deaths - then that's worth discussing. But I don't see any value in applying an unreasonably high standard of statistical proof when our best available model of the world suggests there was an increase in deaths and it would actually be far more surprising (and warrant more study) if there wasn't such an increase.

> If your standard for saying that event x caused deaths is that we have a statistically significant direct correlation between event x and excess deaths that year

It isn't.

> Hell, even something like mass shootings probably aren't enough deaths to show up directly in death numbers for the year.

Yes, there's (probably) no statistically significant link between mass shootings and excess deaths (maybe with the exception of school shootings and excess deaths in the population of school children). But you can directly link 'a shooting' and 'a death', so you don't need to look at statistics to work out if it's true that shootings cause deaths. Maybe if mass shootings started to show up in excess deaths numbers, we'd see a different approach to gun ownership, but that's a separate discussion. You can't do the same with 'closing airspace' and 'deaths on the road'.

When you're looking at a big event like this, there's a lot of other things that can happen. People could be too scared to take trips they might otherwise have taken (meaning a reduction in mileage as folks are not driving to the airport), or the opposite, 9/11 might have inspired people to visit family that they otherwise might not have visited (meaning in increase in mileage). Between 2000 and 2003, the price of gas went down, which might have encouraged people to drive more in general, or to choose to drive rather than fly for financial reasons (although if you wanted to mark that down as 'caused by 9/11' that's probably an argument you could win). You can throw ideas out all day long. The way we validate which ideas have legs is by looking at statistical significance.

Here's some more numbers for you, in 2000, there were 692 billion revenue passenger miles flown in the US. In 2002, it was 642 billion. So we can roughly say that there were 50 billion fewer miles flown in 2002. But the actual number of miles driven in 2002 was 100 billion higher than in 2000 (and note, this is vehicle miles, not passenger miles, whereas the airline numbers are counting passengers). So clearly something else is at play, you can't (only) attribute the increase in driving to people driving instead of flying.

> If you actually think the causal chain breaks down - that 9/11 didn't actually lead to fewer people flying, or that actually didn't lead to more people driving, or that extra driving didn't actually lead to more deaths - then that's worth discussing

I believe that the causal chain does exist but it's weakened at every step. Yes, I think 9/11 led to fewer people flying, but I think that only a proportion of those journeys were substituted for driving, and some smallish percentage of that is further offset by fewer journeys to and from the airport. I think that the extra driving probably did lead to a small number of additional deaths, but again this question of 'is one additional death enough for you to think I'm wrong' comes back.

If I throw aside all scientific ways of looking at it, my belief is that in terms of direct causation, probably, in the 12 months following 9/11, somewhere between 50 and 500 people died on the roads who would not have died on the roads if 9/11 had not happened. But a lot of those were travelling when the airspace was not closed.

If we look at the number of people who died because they made a trip by car that they would have otherwise made by plane but couldn't because US airspace was closed (i.e. on 9/11 itself and during the ground stop on the 12th), you're looking at what I believe to be a very, very small number of people, maybe even zero.