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

12

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

13

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

14

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

15

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

16

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

17

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

18

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

19

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

20

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%

21

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

22

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