Major transport accidents in Norway:
assessing long-term frequency and
priorities for prevention
TRB paper 06-0147
Rune Elvik
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?
2
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
3
Major transport accidents in Norway 1970-2001
450
423
Number of major accidents and fatalities
400
360
350
300
250
Accidents
Fatalities
200
150
85
100
56
50
21
13
4
25
0
Aviation
Railways
Road transport
Maritime
Mode of transport
4
Major transport accidents in Norway 1970-2001
7
6
Accidents per year
5
4
3
2
1
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
5
Major transport accidents occur randomly
10
8.8
Number of years with 0, 1, etc accidents
9
8
8.7
8
8
7
7
5.7
6
5
5
Observed
Poisson
4.5
4
3
2.7
3
2
1.1
1
1
0.5
0
0
0
1
2
3
4
5
6
Number of accidents per year
6
Road accident fatalities (all fatal accidents) in Norway 1970-2004
600
Number of fatalities per year
500
400
300
200
100
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
7
Fatalities in rail transport (all fatal accidents) in Norway 1970-2004
50
45
Number of fatalities per year
40
35
30
25
20
15
10
5
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
8
Aviation fatalities in Norway (all fatal accidents) 1970-2004
160
140
Fatalities per year
120
100
80
60
40
20
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
9
Maritime fatalities in Norway 1970-2003. Recreational boats included
300
250
Fatalities per year
200
150
100
50
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
10
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
0.90
0.80
0.78
Number of accidents per year
0.70
0.70
0.66
0.59
0.60
0.50
0.50
0.50
Observed frequency
Estimated long-term frequency
0.40
0.30
0.20
0.13
0.10
0.10
0.00
Maritime
Aviation
Rail
Road
12
FN-curves for long-term frequency of major transport accidents in Norway
F (accidents per year)
1.000
0.100
Maritime
Aviation
Rail
Road
0.010
0.001
1
10
100
1000
N (fatalities)
13
Probability of 0, 1 etc major accidents per year - low and high estimate
0.40
0.35
0.30
Probability
0.25
Low estimate
0.20
High estimate
0.15
0.10
0.05
0.00
0
1
2
3
4-
Number of major accidents per year
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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
15
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 singlefatality accidents
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Value of fatalities prevented
Utility functions for policy objectives
Reducing
high risk
Reducing
total fatalities
Preventing major
accidents
Number of fatalities prevented
17
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%
20
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
21
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
22