Thursday, October 27, 2011

Safety: Flying vs. Driving

I'm taking a rest from politics today to add to the never-ending debate about flying versus driving. The following appeared in the Times in 1994, though I came across it just recently:
 
To the editor,
 
The editorial "Concern Over Airline Safety (Nov. 16, 1994) perpetuates a myth that has surfaced periodically for years. That is that "flying is still safer than driving to the airport."
 
Not true. The only acceptable method to compare risk between air travel and automobile travel is based on the number of deaths per hour of exposure.
 
Data from a respected safety analyst, Trevor Kletz, show that air travel has a fatal-accident frequency rate four times higher than that for driving a car. For airplane travel there are approximately 2.4 deaths per million hours of exposure; for travel by car the figure is 0.6 deaths per million hours of exposure.
 
Simply put, for the same number of hours riding in a car or riding in an airplane, you are four times more likely to be killed in an airplane than in a car.
 
JOHN M. HOFFMANN
President Safety Engineering Labs Inc.
Detroit, Nov. 22, 1994
 

Here is my take on this. I don't agree that "this is the only acceptable method to compare risk," though it is a method. You have to ask what it is you must or want to worry about.
 
1. If you must go from NY to Chicago, say, and you are concerned about your safety, then you should fly. Here's a simple estimate: A good flying time, NY -> O'Hare, is about 2:15. The driving distance is about 800 miles. Even if you averaged 65 MPH that's still over 12 hours of driving, or more than 4 times as much exposure than in a plane. Since a plane is only 4 times more dangerous per hour, then there you have it: fly. 
 
2. On the other hand, calculations of risk for flying are averages over all carriers and all routes. Presumably this includes Berzerkistan (a Doonesbury creation) Airways flights from a primitive airport north of Irkutsk to the cliffside airport just outside Lima Peru, during Monsoon season. The figures for car travel might also include the short-lived driving career of Sam "five-more-for-the-road" Teetotaler who only drove (past tense) at night. The difference is, you have little control over a flight other than the choice of carrier (and not always that); in a car, on the other hand, you can control how you drive: your physical condition and that of your car, as well as the hours during which you drive. You can actually improve your odds considerably when you drive by being very careful.
 
3. If you are worried about worrying (this is not a joke), then you have to think carefully about how you worry. It is not unreasonable to fear flying, so if you do, and if the prospect of flying is likely to ruin your trip, then drive or take a train. On the other hand, if you worry about driving and find flying exciting (as I do), then fly.
 
4. If you are concerned about ecology/energy the situation is complicated. The US government (http://cta.ornl.gov/data/tedb26/Spreadsheets/Table2_14.xls and http://cta.ornl.gov/data/tedb26/Spreadsheets/Table2_13.xls) gives the following BTU/Passenger-Mile figures:
 
                 Auto          3600
                 Air             4000
                 Rail           3000
 
(I have no idea if these are correct -- they are what the Feds tell us.)
 
The problem with these figures is that they were obtained by dividing the BTU/Mile averages for cars, planes and trains by some sort of estimate of passengers per vehicle. This can be tricky. The "average" car can seat probably 5 people but rarely does. The average plane these days is pretty much packed, but not so the average intercity train. Thus, these estimates are debatable. I'd prefer to tax carbon, let gas prices rise, and let the market sort it out. I also don't have much hope that a realistic energy policy will emerge from our government in the foreseeable future.
 

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