Content Is Safety-In-Numbers (SIN) for fatal bicycle Background - PDF document

Content Is Safety-In-Numbers (SIN) for fatal bicycle • Background crashes confounded by • Study on cycling safety in countries and Dutch municipalities the general level of road • Conclusions and discussion safety? Paul Schepers Ministry of Infrastructure and the Environment Ministerie van Verkeer en Waterstaat 2 October 2017 Jacobsen who coined the term Safety in Numbers Dataset for 18 countries used in the current (SIN) in 2003 study: similar picture • Cycling in 14 European countries • SIN: more cycling � lower risk for cyclists Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 3 October 2017 4 september 14th October 2017 Alternative explanation via road safety? Alternative explanation via road safety? Road Poor road safety and accordingly safety -less cycling High level of road -higher risk for safety and cyclists accordingly: Bicycle Bicycle -more cycling use accidents -lower risk for cyclists Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 5 september 14th October 2017 6 september 14th October 2017

Models used to study SIN How to control for the general level of road safety? Number of cyclist injuries = constant CYCL β 1 MV β 2 e β 3X • Often used proxy is traffic mortality: total road deaths per 100,000 population CYCL Distance cycled or volume of cyclists MV Distance travelled by or volume of motor vehicles X Traffic mortality β 1<1 is indicative of SIN; risk is linear if β 1=1 β 1<1 Injuries β 1=1 CYCL Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 7 september 14th October 2017 8 October 2017 Outcome meta-analysis Elvik and Bjornskau, 2017 Model generally used to study Safety in Numbers, expanded with road safety Number of cyclist injuries = constant CYCL 0.43 MV 0.5 X � If everything else remains the same, doubling the (mortality) amount of cycling results in 35% more cycling injuries: 2 0.43 = 1.35 Cyclist CYCL injuries MV Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 9 september 14th October 2017 10 October 2017 Results for regression for 18 countries; Methodology for area level modelling 7,752 cyclist deaths • Using Negative Binomial regression, the same model is fit on Regression coefficients (95% CI) cyclist deaths in: Parameter Model I Model II – 18 countries Bicycle km ( β 1) 0.40 (0.20 to 0.60) 0.66 (0.52 to 0.80) – 366 Dutch municipalities • Two models: Motor vehicle km ( β 2) 0.55 (0.29 to 0.81) 0.31 (0.16 to 0.46) I. distance travelled by cyclists and motor vehicles II.distance travelled by cyclists and motor vehicles and Traffic mortality 0.12 (0.08 to 0.16) mortality • A change in the in the exponent for distance travelled by AIC 225 204 bicycle ( β 1 in CYCL β 1 ) after adding mortality would indicate SIN is (partially) confounded by the general level of road safety Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 11 september 14th October 2017 12 October 2017

Results for regression for 366 countries; Pooled result of both analyses 1,683 cyclist deaths Regression coefficients (95% CI) Regression coefficients (95% CI) Parameter Parameter Model I Model II Model I Model II Elvik & Bjørnskau, 2017 Bicycle km ( β 1) 0.33 (0.14 to 0.53) 0.58 (0.39 to 0.77) Bicycle km 0.36 0.63 0.43 ( β 1) (0.22 to 0.50) (0.52 to 0.75) (0.33 to 0.53) Motor vehicle km ( β 2) 0.47 (0.27 to 0.68) 0.31 (0.12 to 0.51) Motor 0.50 0.31 0.50 vehicle km (0.34 to 0.68) (0.19 to 0.43) (0.38 to 0.62) Traffic mortality 0.09 (0.07 to 0.12) ( β 2) Traffic 0.10 AIC 1587 1534 mortality (0.08 to 0.12) Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 13 October 2017 14 september 14th October 2017 Conclusions Main practical implication • SIN in area-level models is partially confounded by the general level • Cycling policies to encourage cycling are most effective in of road safety combination with road safety policies if the aim is to increase public health • The higher level of cycling safety in areas with higher cycling participation is partly due to the higher general level of road safety in these areas • After controlling for traffic mortality, there is still a clear indication of SIN with cyclist deaths increasing less than proportional in response to more cycling • We cannot conclude whether or to what degree the remaining SIN effect is causal as control variables for dedicated bicycle infrastructure are lacking in the models Ministerie van Verkeer en Waterstaat Ministerie van Verkeer en Waterstaat 15 september 14th October 2017 16 september 14th October 2017