The Horizons 2020 research project InDev (In-depth Understanding of Accident Causation for Vulnerable Road Users) recently published a handbook with focus on vulnerable road users entitled: How to analyse accident causation? This handbook was developed to help road safety professionals diagnose road safety problems by gaining more insights into the mistakes by road users that lead to collision. It describes various road safety methods that can be applied for studying the safety of vulnerable (and other) road users, including: accident data analysis, conflict and behavioural observations, self-reporting and naturalistic studies and road safety audit and inspection.