Speed is a major factor in overall road safety performance. Excessive and inappropriate speed is accountable for about one third of fatal collisions and is an aggregative factor in most collisions (ETSC, 2019).
In addition to speed in absolute terms, differences in speed (or variation) also have an influence on crash rate. Speed differences result in more encounters among road users and also in more lane-changing and overtaking manoeuvres; both increase the risk of crashes (European Commission, 2021).