Post on 17-Jan-2016
Major transport accidents in Norway: assessing long-term frequency and priorities for
prevention
TRB paper 06-0147Rune Elvik
2
Problems to be discussed
• How many major transport accidents can be expected to occur each year in Norway?
• What is the uncertainty of an estimate of the expected frequency of major transport accidents?
• Can formal techniques for decision analysis help in setting priorities for the prevention of major transport accidents?
3
Major transport accidents
• Five or more fatalities• Historical records for Norway 1970-2001• Historical records for Great Britain 1967-
2001• Historical records for Europe 1991-2003
• Records may not be complete
4
Major transport accidents in Norway 1970-2001
214 13
25
423
56
85
360
0
50
100
150
200
250
300
350
400
450
Aviation Railways Road transport Maritime
Mode of transport
Nu
mb
er
of
ma
jor
acc
ide
nts
an
d f
atal
itie
s
Accidents
Fatalities
5
Major transport accidents in Norway 1970-2001
0
1
2
3
4
5
6
7
1965 1970 1975 1980 1985 1990 1995 2000 2005
Ac
cid
en
ts p
er
ye
ar
6
Major transport accidents occur randomly
5
8 8
7
3
0
1
4.5
8.8 8.7
5.7
2.7
1.1
0.5
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6
Number of accidents per year
Nu
mb
er
of
ye
ars
wit
h 0
, 1
, e
tc a
cc
iden
ts
Observed
Poisson
7
Road accident fatalities (all fatal accidents) in Norway 1970-2004
0
100
200
300
400
500
600
1965 1970 1975 1980 1985 1990 1995 2000 2005
Nu
mb
er o
f fa
talit
ies
per
yea
r
8
Fatalities in rail transport (all fatal accidents) in Norway 1970-2004
0
5
10
15
20
25
30
35
40
45
50
1965 1970 1975 1980 1985 1990 1995 2000 2005
Nu
mb
er o
f fa
tali
tie
s p
er
ye
ar
9
Aviation fatalities in Norway (all fatal accidents) 1970-2004
0
20
40
60
80
100
120
140
160
1965 1970 1975 1980 1985 1990 1995 2000 2005
Fa
tali
tie
s p
er
ye
ar
10
Maritime fatalities in Norway 1970-2003. Recreational boats included
0
50
100
150
200
250
300
1965 1970 1975 1980 1985 1990 1995 2000 2005
Fa
tali
tie
s p
er
ye
ar
11
Some observations
• There is a trend for fatalities to decline in all modes of transport
• The occurrence of a major accident does not signal that safety has deteriorated
• The contribution of major accidents to total fatalities differs substantially between modes of transport
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Observed and estimated long-term frequency of major transport accidents in Norway
0.78
0.66
0.13
0.59
0.70
0.50
0.10
0.50
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Maritime Aviation Rail Road
Nu
mb
er
of
ac
cid
en
ts p
er y
ea
r
Observed frequency
Estimated long-term frequency
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FN-curves for long-term frequency of major transport accidents in Norway
0.001
0.010
0.100
1.000
1 10 100 1000
N (fatalities)
F (
acc
ide
nts
pe
r y
ea
r)
Maritime
Aviation
Rail
Road
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Probability of 0, 1 etc major accidents per year - low and high estimate
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0 1 2 3 4-
Number of major accidents per year
Pro
ba
bili
ty
Low estimate
High estimate
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Conflicting policy objectives
• Maximum reduction of total fatalities• Reducing differences in accident risk• Reducing likelihood of major accidents
• These policy objectives may in principle be weighted by assigning monetary values to them
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Implications of policy objectives
• Reducing total number of fatalities– All fatalities prevented are valued the same
• Reducing differences in risk– Preventing fatalities resulting from high risk is
valued more highly than preventing fatalities resulting from low risk
• Reducing likelihood of major accidents– Preventing several fatalities in one accident is
valued more highly than preventing the same number of fatalities in single-fatality accidents
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Utility functions for policy objectives
Number of fatalities prevented
Va
lue
of
fata
liti
es
pre
ve
nte
d
Reducing total fatalities
Reducing high risk
Preventing major accidents
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A multi attribute utility model
1. (Utility weight for objective 1) x (Outcome indicator for objective 1) +
2. (Utility weight for objective 2) x (Outcome indicator for objective 2) +
3. (Utility weight for objective 3) x (Outcome indicator for objective 3) =Total utility for all objectives
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An illustration for road transport
• Utility weight = attributable risk– All fatalities (objective 1) = 1.000– High risk fatalities (objective 2 ) = 0.340– Major accident fatalities (objective 3) =
0.013• Outcome indicator = value of dimension
– All fatalities (objective 1) = 1.0– High risk fatalities (objective 2) = 5.5 – Major accident fatalities (objective 3) = 6.4
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Total maximum utility (road)
• Overall attainable utility:– (1 x 1) + (0.340 x 5.5) + (0.013 x 6.4) = 2.95
• Contributions of objectives to overall utility:– Reducing total fatalities 1.00/2.95 = 34%– Reducing differences in risk 1.87/2.95 = 63%– Reducing major accidents 0.08/2.95 = 3%
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Discussion of the utility model
• The utility values are arbitrary• The utility function involves double
counting• The utility model does not tell when
benefits are greater than costs
• The utility model is very flexible and can incorporate all policy objectives
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Conclusions
• The long term frequency of major transport accidents is very imperfectly known
• Major accidents occur at random, but are becoming less frequent
• The importance of preventing major accidents can be assessed both in monetary terms and by utility analysis