reasonable to make cost comparison of different means of transportation because
their probabilities can be derived from observed frequencies. For instance, there
have been worldwide 90 to 118 annual airplane accidents between 2009 and 2013
(including 9–13 annual fatal accidents with 173–655 fatalities per year).
2 Based on
the frequencies observed during this period, the probability for a passenger to have
an airplane accident when embarking at the airport is approximately 3 Â 10
−6 .
Road traffic accounts for more than 1 million deaths per year worldwide, mainly
pedestrians and motorcyclists.
3 In a small country like New Zealand, the number of
fatalities due to car crashes has been 254 in 2013. It corresponds to a frequency of
0.8 deaths per 10,000 vehicles.
4 On the basis of 2011–2013 statistics the probability
for a driver to be killed is about 3 Â 10
−9 per km. In 2013, the social cost of fatal
car accident is estimated to NZ$ 4.5 million. The expected cost of fatal accident per
km can be estimated to 0.03 NZ$, that is about one tenth of gas price. Given the
observed frequencies of transport accidents (and assuming the value of loss life is
the same and neglecting the other damage), one can easily compare the social
accident costs of rail, air, maritime and road transportation per km or per travel.
Moreover, data on car accidents can generally be broken down by local area,
models of car, types of roads, age categories of the driver, etc. As a result precise
probability can be estimated according to different situations.
2.2 Nuclear Accident Are no Car Crashes
Estimating probabilities of nuclear accident from frequencies is a non-sense. Since
the first grid-connection of nuclear power plant in 1956 there have been 12
core-meltdowns of reactors, including very limited ones [2]. According to the INES
classification there have been 2 major, or level 7, accidents (Chernobyl and
Fukushima-Daiichi) and 21 accidents with a level equal or higher to 4. Knowing
that since the end 1950s 14,500 reactor-years have passed worldwide the observed
frequencies are 1.6 Â 10
−3 per reactor-year for INES >3; 8.3 Â 10
−4 per
reactor-year for core-meltdown; and 2.7 Â 10
−4 per reactor-year for INES = 7. Is it
sound to infer probabilities from these values? For instance, using a Poisson distribution and knowing that the worldwide nuclear fleet amounts to 435, is it relevant
to say that the probability of an INES 7 accident in 2015 on the planet is 0,11
(i.e., [1−(1–2.7 Â 10
−4 )
435 ]?
No! The reasons are twofold. The obvious one is that the number of observations
is too small. The observed events cannot be assumed as representative. Reactors are
neither identical, nor exposed to the same locational risk (e.g. earthquake, flooding).
2
International Civil Aviation Organization, 2014 Safety Report.
3
World Health Organization, Global Safety Support on Road Safety 2013.
4
Ministry of Transport, Motor Vehicle Crashed in New Zealand 2013.
82
R. Bizet and F. Lévêque
their probabilities can be derived from observed frequencies. For instance, there
have been worldwide 90 to 118 annual airplane accidents between 2009 and 2013
(including 9–13 annual fatal accidents with 173–655 fatalities per year).
2 Based on
the frequencies observed during this period, the probability for a passenger to have
an airplane accident when embarking at the airport is approximately 3 Â 10
−6 .
Road traffic accounts for more than 1 million deaths per year worldwide, mainly
pedestrians and motorcyclists.
3 In a small country like New Zealand, the number of
fatalities due to car crashes has been 254 in 2013. It corresponds to a frequency of
0.8 deaths per 10,000 vehicles.
4 On the basis of 2011–2013 statistics the probability
for a driver to be killed is about 3 Â 10
−9 per km. In 2013, the social cost of fatal
car accident is estimated to NZ$ 4.5 million. The expected cost of fatal accident per
km can be estimated to 0.03 NZ$, that is about one tenth of gas price. Given the
observed frequencies of transport accidents (and assuming the value of loss life is
the same and neglecting the other damage), one can easily compare the social
accident costs of rail, air, maritime and road transportation per km or per travel.
Moreover, data on car accidents can generally be broken down by local area,
models of car, types of roads, age categories of the driver, etc. As a result precise
probability can be estimated according to different situations.
2.2 Nuclear Accident Are no Car Crashes
Estimating probabilities of nuclear accident from frequencies is a non-sense. Since
the first grid-connection of nuclear power plant in 1956 there have been 12
core-meltdowns of reactors, including very limited ones [2]. According to the INES
classification there have been 2 major, or level 7, accidents (Chernobyl and
Fukushima-Daiichi) and 21 accidents with a level equal or higher to 4. Knowing
that since the end 1950s 14,500 reactor-years have passed worldwide the observed
frequencies are 1.6 Â 10
−3 per reactor-year for INES >3; 8.3 Â 10
−4 per
reactor-year for core-meltdown; and 2.7 Â 10
−4 per reactor-year for INES = 7. Is it
sound to infer probabilities from these values? For instance, using a Poisson distribution and knowing that the worldwide nuclear fleet amounts to 435, is it relevant
to say that the probability of an INES 7 accident in 2015 on the planet is 0,11
(i.e., [1−(1–2.7 Â 10
−4 )
435 ]?
No! The reasons are twofold. The obvious one is that the number of observations
is too small. The observed events cannot be assumed as representative. Reactors are
neither identical, nor exposed to the same locational risk (e.g. earthquake, flooding).
2
International Civil Aviation Organization, 2014 Safety Report.
3
World Health Organization, Global Safety Support on Road Safety 2013.
4
Ministry of Transport, Motor Vehicle Crashed in New Zealand 2013.
82
R. Bizet and F. Lévêque