From: jbrown@qdeck.com (Jordan Brown)
Subject: Accident rated (was Re: Corporate reimbursement ...)
Organization: Quarterdeck Office Systems, Santa Monica CA
Date: Wed, 04 Nov 1992 02:16:59 GMT

jbrown@qdeck.com (Jordan Brown) writes:
>peted@microsoft.com (Peter Duniho) writes:
>>jbrown@qdeck.com (Jordan Brown) writes:
>>>somebody writes:
>>>>But which mode of transportation is safer per mile?
>>>Car.  Sorry.
>>Can you justify this statement "Car.  Sorry."?
>... I'll see if I can find some evidence.

Well, here are some figures...
 
First, from the 1992 AOPA Aviation USA statistics page (page 926),
preliminary data for 1990:
 
GA Total Accidents		2138
GA Fatal Accidents		424
GA Fatalities			736
GA Hours Flown			34.8 million
GA Statute Miles Flown		4,827 million
GA Passengers/departure		2.5
 
(Miles flown statistic didn't specify statute or nautical; I generously
assume it was nautical.)
 
Calculated from the above:
 
Average speed			139 sm/hr
Fatality rate			15.2 per 100 million sm
 
Next, from the 1992 Information Please Almanac, a predigested figure:
 
1989 Auto Fatality rate		2.3 per 100 million vehicle miles
 
And some supporting figures:
 
Total travel, all motor vehicles	2,107,040 million miles
Total automobile fatalities		46,900
 
If you do the math by hand you come up with 2.233 fatalities per 100
million vehicle miles, slightly but not outrageously off from the
predigested statistic.
 
Conclusion:  In fatalities per vehicle mile, automobiles are about 6.6
times safer than GA airplanes.
 
AARGH.  I hate that statistic, and I almost fell into the trap of using
it.  It artificially penalizes high-occupancy vehicles, since (one would
think) the fatality rate is roughly proportional to the number of occupants.
Obviously putting two people in the car doesn't make it twice as dangerous
in any intuitive sense, yet with the same number of vehicle miles it will
roughly double the fatality rate.
 
Let's look at a somewhat fairer statistic, fatalities per passenger mile.
To get that, we'll have to guestimate the average occupancy rate for
automobiles.  I'd accept 1.5.
 
				GA		Auto
passenger miles, millions	12,068		3,160,560
fatalities/passenger 100 mil mi	6.1		1.5
 
Conclusion:  In fatalities per passenger mile, automobiles are about
4 times safer than GA airplanes.
 
The best I can come for non-fatal accidents is to extrapolate from a
couple of predigested statistics for auto accidents:  a fatality every
11 minutes and an injury every 19 seconds.  These yield rates of 48,000
and 1.7 million per year respectively.  (Cross-check:  the fatality
figure here and above differ a bit, but within reasonable limits given
the data.)  Unfortunately, we still don't have comparable values - the
airplane value is for total accidents, and the automobile value is for
injuries.  However, we can make up some numbers and proceed.  Given
the above, there were approximately 5345 (= 2138 * 2.5) "accident
passengers".  Given that 736 (= 14%) of them died, it's probably
optimistic to assume that half of them (2672.5 :-) were injured (probably
more than that were injured), and now we have some comparable numbers
and can continue:
 
				GA	Auto
Injuries/100 mil vehicle miles	55	81
Injuries/100 mil pass. miles	22	54
Casualties/100 mil veh. miles	70	83
Casualties/100 mil pass. miles	28	56
 
These values must be taken with an enormous amount of salt, since there
are several very hazy values that went into them. (My estimates of 1.5
passengers/car and 50% of airplane accident passengers being injured are
the major ones.)  The aviation rate casualty rate per 100 million
passenger miles is presumably between 6.1 (all survivors uninjured) and
44 (all passengers injured or killed).  The auto rate is presumably no
more than 83 (1 person/car) and probably no less than 42 (2 people/car).
 
Very Hazy Conclusion:  in casualties/passenger mile, GA airplanes are
twice as safe as automobiles.  (Plausible values range from "as safe"
to "14 times as safe".)
 
So, which is safer?  Probably depends on whether you care about getting
killed or about being injured.  Your chances of being killed, per mile
travelled, are higher in an airplane.  Your chances of being injured
appear to be lower.
 
It would be interesting to look at non-participant fatality rates - people
on the ground killed by airplanes and pedestrians and bicyclists killed
by automobiles, but I don't have either of those figures available so
they will have to remain unknown for now.  Given the relative frequency of
pedestrian fatalities in auto accidents and the relative infrequency of
on-the-ground fatalities in airplane accidents I would suspect that
airplanes would fare better in this comparison then they do in the
participant-fatality comparison.
 
Of course, you can dramatically improve your aircraft accident rate by
not flying while intoxicated and by not flying VFR into IMC, but to
be fair you must also take similar precautions while driving - do not
drive while intoxicated and do not exceed a safe speed for the conditions.
"Speed too fast" was a factor in 26.7% of fatal auto accidents.
 
Other random statistics:  Arkansas is tied for the #2 spot among the states
in motor vehicle deaths at 3.3 per 100 million miles (NM 3.5, AR,MI,NV,WV
all 3.3, average 2.3), and takes the #6 spot in total death rate at
10.2 / 1000 population.  (DC 16.3(!), MO 10.8, FL 10.6, WV 10.5, PA 10.3,
average 8.6) (CA 2.1 and 7.5 resp.)
 
Your Mileage May Vary.
Newsgroups: rec.aviation.misc