The turning point in the number of traffic fatalities: two - PDF document

The turning point in the number of traffic fatalities: two hypotheses about changes in underlying trends ICTCT Workshop, Karlsruhe, October 16-17, 2014 Submitted to Accident Analysis and Prevention Ulf Brüde (VTI) and Rune Elvik (TØI) Relative changes in the number of traffic fatalities in six motorised countries - all-time peak number = 100 120.0 Relative number of traffic fatalities - all-time high = 100 100.0 United States 80.0 Great Britain 60.0 Denmark Sweden Norway 40.0 Netherlands 20.0 0.0 1940 1950 1960 1970 1980 1990 2000 2010 2020 United States Great Britain Netherlands Sweden Denmark Norway Page 2

Two hypotheses about the turning point � Hypothesis 1 (due to Oppe): � There never was any real turning point � Long-term trends were the same before-and-after � Hypothesis 2: � The underlying trends changed from before to after the turning point � In particular, fatality rate declined at a faster rate � Which are the trends we are talking about? � Annual traffic growth � Annual decline in fatality rate (fatalities per billion vehicle kilometre) Page 3 A turning point following from stable underlying trends 2.000 16.000 Fatalities reach peak values in Relative fatality rate and number of fatalities (first year = 1.0) 1.800 years 17 and 18 14.000 1.600 Relative traffic volume (first year = 1.0) 12.000 1.400 Year 2 = 15.0% 10.000 1.200 Year 3 = 15.0 • 0.97 = 13.8% Year 4 = 13.8 • 0.97 = 12.8% Traffic growth slows Year 5 = 12.8 • 0.97 = 11.8% 1.000 8.000 down by 3 % each year 0.800 6.000 0.600 4.000 0.400 Fatality rate declines by 5 % per year the whole period 2.000 0.200 0.000 0.000 0 10 20 30 40 50 60 70 Year Fatality rate Fatalities Traffic volume Page 4

How can we determine the stability of trends? � Fit functions to determine trends before turning point � Predict number of fatalities after turning point based on trends before turning point � If predictions are accurate, trends before the turning point continued after the turning point � Conclusion: trends were stable � If predictions are not accurate, trends before the turning point did not continue after it � Conclusion: trends were not stable � Further conclusion: turning point could not have been predicted based on trends before it occurred Page 5 Number of traffic fatalities in Norway 1952-2013 and two models describing long-term development 700 Model fitted to data for 1952-1970 Model extrapolated to 1971-2013 (solid line) (solid line) 600 500 Annual number of fatalities 400 300 Model fitted to data for 1952-2013 (dashed line) 200 100 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 6

Percent annual growth in traffic volume in Norway and two models describing long-term development 20.0 18.0 Model fitted to data for 1952-1970 (solid line) Percent annual growth in vehicle kilometres of travel 16.0 14.0 12.0 10.0 8.0 6.0 Model fitted to data for 1952- 4.0 2013 (dashed line) 2.0 Model extrapolated to 1971-2013 (solid line) 0.0 1950 1960 1970 1980 1990 2000 2010 2020 -2.0 Year Page 7 Fatality rate in Norway 1952-2013 and two models describing long-term development 100.00 Model fitted to data for 1952-2013 (dashed line) 90.00 Fatalities per billion vehicle kilometres of driving 80.00 70.00 60.00 50.00 Model fitted to data for 1952-1970 Model extrapolated to 1971-2013 40.00 (solid line) (solid line) 30.00 20.00 10.00 0.00 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 8

Study of six countries � Denmark (1950-2012) � Great Britain (1949-2011) � Netherlands (1948-2010) � Norway (1952-2013) � Sweden (1950-2012) � United States (1948-2012) � These countries were selected because: � They have all experienced a turning point around 1970 � The have data on vehicle kilometres going back to about 1950 Page 9 Annual number of traffic fatalities in Denmark and two models describing long-term development 1400 1200 Model fitted to data for Model extrapolated to 1000 1950-1971 (solid line) 1972-2012 (solid line) Annual number of fatalities 800 Model fitted to data for 1950- 2012 (dashed line) 600 400 200 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 10

Annual number of traffic fatalities in Great Britain 1949-2011 and two models describing long-term development 20000 18000 Model extrapolated to 16000 1967-2011 (solid line) 14000 Annual number of fatalities 12000 Model fitted to data for 10000 1949-1966 (solid line) 8000 Model fitted to data for 1949- 2011 (dashed line) 6000 4000 2000 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 11 Number of traffic fatalities in the Netherlands 1948-2010 and two models describing long-term development 4500 4000 3500 Model extrapolated to Annual number of fatalities 3000 1973-2010 (solid line) Model fitted to data for 1948-1972 (solid line) 2500 Model fitted to data for 1948- 2010 (dashed line) 2000 1500 1000 500 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 12

Number of traffic fatalities in Sweden 1950-2012 and two models describing long term development 1400 Model fitted to data for 1950-1966 (solid line) 1200 Model fitted to data for 1950- 2012 (dashed line) 1000 Annual number of fatalities 800 600 Model extrapolated to 400 1967-2012 (solid line) 200 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 13 Annual number of traffic fatalities in the United States 1948-2012 and two models describing long term development 140000 120000 Model extrapolated to 1973-2012 (solid line) 100000 Annual number of fatalities 80000 Model fitted to data for 1948-1972 (solid line) Model fitted to data for 1948- 2012 (dashed line) 60000 40000 20000 0 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Page 14

Changes in trends from before to after turning point 15.0 11.9 10.6 10.2 9.7 10.0 8.0 Mean annual percentage change 6.6 5.1 4.9 4.4 4.2 5.0 3.4 3.1 2.9 2.4 2.3 2.2 2.1 2.0 0.0 -1.2 -1.9 -2.3 -2.8 -3.0 -3.1 -3.3 -3.6 -3.8 -5.0 -4.3 -4.6 -5.0 -5.3 -5.2 -5.5 -5.8 -6.1 -6.7 -10.0 Traffic growth before Traffic growth after Fatality rate before Fatality rate after Net trend before Net trend after Mean trends before and after turning point Denmark Great Britain Netherlands Norway Sweden United States Page 15 Concluding comments � The turning point in the number of traffic fatalities is common to most highly motorised countries � In theory, a turning point could occur even if the long-term trends determining the number of fatalities remain unchanged � For the countries included in this study, there is stronger evidence for a change in trends than for stable trends � The most important contributing factor is a slowdown of traffic growth � The decline in fatality rates has increased in some countries, but not all Page 16