Major transport accidents in Norway: assessing long-term frequency and priorities for prevention Rune Elvik, Institute of Transport Economics, Oslo, Norway
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 Number of major accidents and fatalities 450 400 350 300 250 200 150 100 50 0 423 360 85 56 21 25 13 4 Aviation Railways Road transport Maritime Mode of transport Accidents Fatalities 4
Major transport accidents in Norway 1970-2001 7 6 5 Accidents per year 4 3 2 1 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 5
Major transport accidents occur randomly 10 9 8.8 8.7 Number of years with 0, 1, etc accidents 8 7 6 5 4 3 2 1 0 5 8 8 7 5.7 4.5 3 2.7 1.1 1 0.5 0 0 1 2 3 4 5 6 Observed Poisson Number of accidents per year 6
Road accident fatalities (all fatal accidents) in Norway 1970-2004 600 500 Number of fatalities per year 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 40 Number of fatalities per year 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 160 140 120 Fatalities per year 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 11
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 0.60 0.50 0.40 0.30 0.20 0.10 0.70 0.66 0.50 0.13 0.10 0.59 0.50 Observed frequency Estimated long-term frequency 0.00 Maritime Aviation Rail Road 12
FN-curves for long-term frequency of major transport accidents in Norway 1.000 F (accidents per year) 0.100 0.010 Maritime Aviation Rail Road 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 0.20 0.15 Low estimate High estimate 0.10 0.05 0.00 0 1 2 3 4- Number of major accidents per year 14
Conflicting policy objectives Maximum reduction of total fatalities Reducing differences in accident risk Reducing likelihood of major accidents These policy objectives cannot be reconciled 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 single-fatality accidents 16
Utility functions for policy objectives Value of fatalities prevented Reducing high risk Reducing total fatalities Preventing major accidents Number of fatalities prevented 17
A three dimensional representation Risk Number of fatal accidents Number of fatalities per accident 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 cannot be addressed by means of cost-benefit analysis 23