Air vs. ground travel
John Whittington
>Paul.Be...@m.cc.utah.edu (Paul Bernhardt) writes:
>
>>I recall a statistic from a decade or so back that went like this:
>>"Half of all traffic accidents happen within 25 miles of home." The
>
>No, it's most accidents happen within 5 miles of home
>and at speeds of under 25 miles per hour.
One assumes, as Paul was attempting to estimate, that this is primarily due
to the fact that a high proportion of journies (and passenger-miles!) do
fall into this category. Another factor, as discussed by myself and others
elsewhere in this thread, is that the portions of journey near to home are
likely to be those on the most hazardous roads (intersections, pedestrians
etc.). Exactly the same argument has been used extensively in the UK to
encourage the wearing of seat belts even for short journies.
John
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John Whittington
>I've been telling people about this "miles" nonsense for years!
>I do suspect that if I want to drive from, say San Francisco
>to Chicago, that it may in fact be safer than flying -- for a
>single person.
Ed and I seem agreed on this one!
>If I want to move a group along the
>same route (of say 200 people) flying is the better option. I
>wish the data was broken out in such a way as to examine this
>difference, but it isn't as far as I have seen.
I find this much more difficult to believe. Assume that the risk of a
single person perishing during the journey from San Franscisco to Chicago is
identical with both driving and flying - say p1.
Now consider that you have 200 people to make the journey. If driving (if
the risks to each individual will be assumed to be independent), the
probability of all 200 perishing would be p1^200 - a very small number. The
same would be true if they all travelled in SEPARATE aircraft. However, if
they all travelled in the same aircraft (with non-independent risks) would
not the risk of all 200 perishing still be p1?
It seems to me that Ed may have it round the wrong way, since risks on the
road are independent, whereas those in a plane are not. The risk to an
individual is obviously not influenced by the size of the group of
travellers one is considering. However, the risk to the group as a whole
(or any proportion of it) will be influenced by the number travelling in
each vehicle (air or road).
As regards the other evolving part of this thread about the nature of risks
with car travel, the situation is clearly much more complex than air travel
(when virtually all risks are concentrated during landing and take off), as
I indicated in my earlier post. In some respects, long distance road travel
may have some of the features of air travel - with the greatest risk 'at the
ends' of the journey, when one is negotiating urban traffic with many
intersections etc., but much less on the bulk of the journey along major
highways. Risk is certainly not going to be a linear function of distance
travelled unless one is driving on the same type (etc.) of roads throughout.
Driver fatigue may introduce some degree of a linear element.
All-in-all, I stick to my original view that one probably needs to work in
terms of the risk per 'person-journey' on a particular journey from specific
A to B. I also suspect that one needs to take into account the road travel
element involved in virtually any journey. I would guess that the risk of
death is probably often greater during road journies to/from the airports
than during the flight itself.
.. just my continuing thoughts!
Ed Russell
- >I do suspect that if I want to drive from, say San Francisco
- >to Chicago, that it may in fact be safer than flying -- for a
- >single person.
>
> Ed and I seem agreed on this one!
- >same route (of say 200 people) flying is the better option. I
- >wish the data was broken out in such a way as to examine this
- >difference, but it isn't as far as I have seen.
>
> I find this much more difficult to believe. Assume that the risk of a
> single person perishing during the journey from San Franscisco to Chicago is
> identical with both driving and flying - say p1.
>
> Now consider that you have 200 people to make the journey. If driving (if
> the risks to each individual will be assumed to be independent), the
> probability of all 200 perishing would be p1^200 - a very small number. The
> same would be true if they all travelled in SEPARATE aircraft. However, if
> they all travelled in the same aircraft (with non-independent risks) would
> not the risk of all 200 perishing still be p1?
>
Ah, I guess I left out my assumption: charter flight vs have to take lots
of cars. So with the charter flight -- everyone is safe with prob 1-p1.
With the cars everyone is safe with prob (1-p1)^k where k=num of cars....
under an assumption of independence of accidents.
You do bring up the more interesting point though -- in the cars, the odds
of everyone perishing is very small, while in the plane it is higher. So
obviously air carrier proponents of moving large groups are not using mini-max
concepts....
One has to wonder why we wouldn't use mini-max concepts in travel since we seem
to do that with so many other safety/health regulations?
Regards, Ed.
Meredith...@charlesview.com
<<You do bring up the more interesting point though -- in the cars, the odds
of everyone perishing is very small, while in the plane it is higher. So
obviously air carrier proponents of moving large groups are not using mini-max
concepts....
One has to wonder why we wouldn't use mini-max concepts in travel since we
seem to do that with so many other safety/health regulations?>>
Actually, I know some married couples with children where the parents
will not take the same flight, just for that reason - I guess parents
need to be intuitive probabilists :-)
John Whittington
>One has to wonder why we wouldn't use mini-max concepts in travel since we
>seem to do that with so many other safety/health regulations?>>
>
>Actually, I know some married couples with children where the parents
>will not take the same flight, just for that reason - I guess parents
>need to be intuitive probabilists :-)
Indeed, and we have tended to behave like that too - parents do not fly
together unless the children are on the same flight as well. However, it is
probable that we should apply the same principle to car travel, although we
certainly don't. This thread has concentrated on the comparison of 200
people in one aircraft vs. 200 people in 200 cars. But what about 200
people in 100 cars - the risk of both occupants of a car perishing are then
relatively high; a car crash which kills one occupant of a car very
frequently also kills a second occupant. The lack of independence is not
quite as dramatic as with flying, but it's still a major factor.
John Whittington
>You do bring up the more interesting point though -- in the cars, the odds
>of everyone perishing is very small, while in the plane it is higher. So
>obviously air carrier proponents of moving large groups are not using mini-max
>concepts....
>
>One has to wonder why we wouldn't use mini-max concepts in travel since we seem
>to do that with so many other safety/health regulations?
I think that, in deciding how to act, people DO (at least subconsciously)
usually apply such concepts. It has already been mentioned that some pairs
of parents chose not to fly in the same aircraft. The British monarch and
heir to the throne never travel in the same aircraft - and the same may be
true of the President and Vice-President of the USA? Many companies would
be hesitaant to put all their key people on one plane ... etc.
One serious breach of this principle happened in the UK a couple of years
ago - when a ridiculous number of the top people in the UK anti-terrorist
service perished in a helicopter crash.
Meredith...@charlesview.com
<<As an additional point to John's message, most (if not all)
professional sports teams in North America travel on separate planes.
However, there may be underlying reasons such as potential conflict.>>
This probably harkens back to the crash about 30 years ago of a plane
containing the entire US Olympic figure skating team and their
coaches. This was devastating for American figure skating for the
next many years.
Meredith
John Whittington
>This probably harkens back to the crash about 30 years ago of a plane
>containing the entire US Olympic figure skating team and their
>coaches. This was devastating for American figure skating for the
>next many years.
.. and those of us old enough over here remember when the majority of our
Manchester United football team were lost in a crash in Munich - again, I
think, about 30 years ago.