Differences between countries in their road safety levels and over-time developments, may by and large be traced back to (combinations of) four, partly related factors      :
- Differences in prosperity level and culture.
- Differences in mobility and travel behaviour.
- Differences in road safety policies.
- And the related differences in underlying performance indicators for the safety of roads, vehicles, road users and assistance.
Differences in prosperity level and culture
Van den Berghe et al.  show that the more prosperous countries have higher road safety levels than less prosperous countries. They also found that countries with a more individualistic culture – people whose opinion is not formed by being members of a social group – have higher road safety levels. In addition, historical, geographic and climatic differences have a more structural effect on matters like spatial planning, development of the road network, mobility and traffic mix, and thus on road safety levels.
Differences in mobility and travel behaviour
Countries differ in e.g. car density, bicycle use, the share of freight traffic or agricultural traffic; this also affects road safety . Thus, the Netherlands have a relatively large number of bicycles, which are not only used for recreational purposes, but also for daily rides (shopping, school, work). Since cycling is a vulnerable mode of transport, this affects the total number of casualties (also see the question How does the Dutch number of road deaths for the most important transport modes compare to these same numbers elsewhere?)
Differences in road safety policy
Several researchers point to differences in policy, policy priorities and governance to explain road safety differences between countries. Bliss & Breen  distinguish seven relevant aspects: co-ordination, legislation, funding, promotion, monitoring/evaluating, research and knowledge dissemination. Chen et al. 
distinguish five factors that contribute to the quality of national road safety policies: scope and ambitions of road safety targets, sensible problem analysis prior to policy making, economic evaluation of proposed policies, monitoring of road safety policies, and clearly laid down responsibilities in support of policy implementation. The road safety policies eventually result in a set of road safety measures consisting of legislation, infrastructural measures, vehicle measures, enforcement, education and public service advertising.
Differences in safety indicator scores
Together, the three previously mentioned factors determine national performance according to the relevant safety indicators (Key Performance Indicators – KPIs; also called safety performance indicators – SPIs) for vehicles, infrastructure, road user behaviour and assistance  . In benchmark studies, road safety differences between countries (or regions) are mostly explained by differences in performance indicators : if a country has a relatively large number of road casualties, this often relates to poor performance according to one or more indicators. Examples are: more speeding than in other countries, helmets worn less often, or a less safe infrastructure layout.