Psychoactive substance use and other driver-related risk factors of road traffic injury: An epidemiological study of associations, trends, and crash characteristics Thesis for the degree of Philosophiae Doctor (PhD) Anja Valen Department of Forensic Sciences Division of Forensic Sciences Faculty of Medicine © Anja Valen, 2021 Series of dissertations submitted to the Faculty of Medicine, University of Oslo ISBN 978-82-8377-819-9 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Cover: Hanne Baadsgaard Utigard. Print production: Reprosentralen, University of Oslo. Tableofcontents Summary.....................................................................................................................................VI Acknowledgements..............................................................................................................VIII Acronyms,abbreviations,andterminology.....................................................................X Listofpapers............................................................................................................................XII Overviewofthisthesis........................................................................................................XIII 1Introduction.............................................................................................................................1 1.1 Risk factors of road traffic injury ............................................................................................. 2 1.1.1 Haddon Matrix ......................................................................................................................... 2 1.1.2 Human risk factors ................................................................................................................. 4 1.1.3 Vehicle-related risk factors ................................................................................................. 8 1.1.4 Environmental risk factors ................................................................................................. 9 1.1.5 Aspects regarding traffic injury prevention ............................................................. 11 1.2. Substances that may increase the risk of a road traffic crash .................................. 13 1.2.1 Alcohol ...................................................................................................................................... 14 1.2.2 Cannabis .................................................................................................................................. 14 1.2.3 Stimulants ............................................................................................................................... 15 1.2.4 Medicinal drugs .................................................................................................................... 17 1.2.5 Combined substance use .................................................................................................. 19 1.3 Global trends in fatal road traffic crashes ......................................................................... 21 1.4 Situation in Norway .................................................................................................................... 23 1.4.1 Trends in road traffic injuries and deaths ................................................................. 23 1.4.2 Important changes in road safety policies ................................................................ 25 1.4.3 DUI laws and enforcement ............................................................................................... 26 1.5 Current knowledge gaps ........................................................................................................... 29 2Aimsofthestudy.................................................................................................................31 3Materialandmethods........................................................................................................32 3.1 Funding ............................................................................................................................................ 32 3.2 Sources of data .............................................................................................................................. 32 3.2.1 Papers I and II ....................................................................................................................... 32 3.2.2 Papers III and IV ................................................................................................................... 32 III 3.3 Ethical and legal aspects ........................................................................................................... 33 3.4 Study design ................................................................................................................................... 35 3.5 Statistical methods ...................................................................................................................... 35 3.5.1 Descriptive and inferential statistics ........................................................................... 35 3.5.2 Statistical tests ...................................................................................................................... 36 3.6 Software ........................................................................................................................................... 37 4Summariesofresults.........................................................................................................38 4.1 Paper I............................................................................................................................................... 38 4.2 Paper II ............................................................................................................................................. 40 4.3 Paper III ........................................................................................................................................... 41 4.4 Paper IV ............................................................................................................................................ 43 4.5 Additional results ........................................................................................................................ 45 4.5.1 Alcohol results including drivers suspected of only alcohol use ..................... 45 4.5.2 THC concentrations ............................................................................................................ 47 5Discussion..............................................................................................................................49 5.1 Trends in psychoactive substance use ................................................................................ 49 5.1.1 Prevalence among drivers arrested or killed ........................................................... 49 5.1.2 Trends among arrested drivers ..................................................................................... 52 5.1.3 Trends among killed drivers ........................................................................................... 60 5.2 Driving errors and characteristics of impaired versus sober killed drivers....... 62 5.2.1 Risk factors associated with drug/alcohol impairment ...................................... 62 5.2.2 Risk factors not associated with drug/alcohol impairment .............................. 65 5.2.3 Crash characteristics .......................................................................................................... 66 5.3 Possible reasons for declining road death numbers ..................................................... 67 5.3.1 Trends in crash characteristics ...................................................................................... 67 5.3.2 Trends in unsafe driving behaviours ........................................................................... 68 5.3.3 Age and sex trends .............................................................................................................. 71 5.4 Methodological considerations .............................................................................................. 73 5.4.1 Study design ........................................................................................................................... 74 5.4.2 Internal validity .................................................................................................................... 75 5.4.3 External validity ................................................................................................................... 81 6Conclusionsandfutureperspectives...........................................................................85 IV 6.1 Conclusions .................................................................................................................................... 85 6.2 Future perspectives .................................................................................................................... 86 7References.............................................................................................................................89 8Appendices..........................................................................................................................115 V Summary Driving a motor vehicle is a complex task, and the driver’s consumption