I think I'm making a distinction between using it colloquially (i.e. I can say that my uncle is tall, which can be true, but it doesn't tell you much about my uncle's actual height) and using it with the rigor that Bezzi implied (i.e. "has someone studied this clear category of cautious drivers"?)

Then again, my example here seems to have failed because people do study tallness: https://www.sciencedirect.com/science/article/abs/pii/000291499390523F , but they crucially define tallness as above the 95th percentile. Other studies I'm glanced at use height as a continuous variable, so who the heck knows. 

Yeah, okay. 

Look at me thinking like an engineer - "but it's not useful from a practical point of view because we don't have access to that data".

I think the thing you're missing is you're still exposed to crashes because of some maniac doing something extremely risky and hitting you.

I'm also a very cautious driver (as you can imagine in my line of work), but I do make mistakes all the time. 

This paper seems like it might be interesting for you to read: https://www.pnas.org/doi/epdf/10.1073/pnas.1513271113 

I've just had a skim but here's some of my impressions. I might read it in more detail when I get to work today.

It doesn't deal with fatalities (just crashes) but having a quick look at Fig 1, drivers who aren't distracted or impaired are involved in ~28% of crashes. Note that "impairment" also includes things like anger. 

Fig 2 is pretty great for you - shows the baseline of each type of impairment, error, distraction and the odds ratio for crashes it's involved in. Not a statistician but I believe that means you're 10 times more likely to get into a crash if you're visibly angry/sad but only 3 times more likely if you're drowsy. Which is very interesting to know.

And that 51% of drivers are observed to be distracted in some way during normal driving condition (which can include "dancing in seat to music" and "interaction with adult passenger". 

This paper was just the first result in a scholar search for the term "crash causation factors driver", so this info is relatively easy to find.

"Passenger mile" is not a stat we use in my jurisdiction (we use VKT, vehicle kilometres travelled), but if I'm interpreting it right, then you need to know the average number of passengers to know the number of crashes the driver is involved in. For example, say that each bus has 10 passengers on average, that would put the fatalities per passenger mile at 0.80, which given this is OOM seems pretty similar to cars.

That said, following that to its conclusion you'd end up with trains having some horrendously high rate of crashing, which doesn't pass the sniff test. I think I might be having a failure of logic somewhere here.

I mean it doesn't describe something objective/measurable unless you define it explicitly in terms of behaviours. People can do research on e.g. crash rates for drivers who never drink and drive vs frequently drink and drive, people who speed and people who don't, etc. 

I can't believe you've never heard the stereotype that taxi drivers aren't safe drivers.

I don't know about proxies for "careful driving". That is not my area of expertise. 

That said, it's well-known that professional race car drivers die in car crashes at higher rates during their general driving (I don't fancy digging up a citation; you can google it yourself).

I always think of the old chestnut that something like eighty percent of people think they're above average at driving. 

I attended a training course recently that stated that educating drivers about the dangers of texting while driving is not very useful, as everyone thinks that they are careful with how and where they choose to text (e.g. only while stopped), but they agree that other drivers shouldn't. Apparently, they reckon it's most effective to tell people "if you text and drive, your kids will grow up to text and drive too". Psychology, eh?

I think all of those are very illustrative of the biases people have in how perceive their operation of their vehicles. 

I am relatively convinced that 95% of crashes involve a variety of factors contributing (swiss cheese model). There is rarely, if ever, only one thing that causes a serious crash. As a road safety professional, then, my duty is to make sure that the road forgives any human errors. Safe Systems is the current philosophy in road safety, which states that nobody should be seriously injured or die on the road, even though people do make mistakes. And they do. All the time.

https://acrs.org.au/files/arsrpe/RS050099.pdf <- there's a paper that covers your exact question (comparing crashes in taxis and passenger cars. in case you don't know the terminology, "fleet vehicle" refers to cars that are registered as work cars for an organisation, so more likely to be people on their "best behaviour" as far as drinking/speeding/etc)

Table 5 in particular, per 100 million vehicle kms travelled you have taxis having about half as many fatal crashes as cars but about 50% more injury crashes and maybe 10% more towaway crashes (eyeballing it)

Table 10 also shows that some 30% of taxi drivers involved in crashes weren't wearing seat belts (they're apparently not legally required to in NSW! news to me), which is a pretty big clue that taxi drivers aren't the paragon of careful driving one might assume.

"Cautious driver" is not a real category. It's not something my crash database can filter on. 

You make mistakes when you drive. We all do. It is human nature, and driving is a complex chain of tasks.

If you never speed, never drive after even one drink, never break a single road rule, know every single road rule (in my jurisdiction the road traffic code is some 400 pages long!), never take gaps in traffic that are too close, never go through an orange light too late, never jaywalk, always ensure your car is mechanically up to date, etc etc etc, then you are either pathological about your rule following or a liar. 

I do crash analysis as part of my job, almost every day. I can tell you there are PLENTY of bus crashes - buses going before the passengers were sat down resulting in minor injuries, buses hitting pedestrians resulting in hospitalisation, heck I was in a bus about a year ago that rear-ended a car in front of it. I only have access to data in one jurisdiction and I don't believe that data includes taxis, uber drivers, etc. Anecdotally my uber drivers often adjust the GPS when they're driving and tend to speed so I wouldn't call them particularly cautious.

For the record, as far as I know I don't have the right to pull out my jurisdiction's crash data so I won't be able to respond to specific requests. I do know that "bus" is a category of vehicle we have. I don't know whether taxi is.

EDIT: 
https://www.9news.com.au/national/liverpool-crash-pedestrian-dies-hit-by-bus-sydney-south-west/6eba1c4a-0825-4828-87c1-b530e5e4e2b5 - a man in Sydney died after being hit by a bus a month ago

https://thewest.com.au/news/traffic/perth-crash-man-hit-by-bus-on-wellington-street-as-police-close-road-c-12809596 (paywall i can't bypass) - a man in Perth was hit by a bus last week

seriously I just searched for "pedestrian hit by a bus" and there are SO MANY in Australia. With a cursory search I see three in Perth (2 million in the greater metro area) in the last six months.