The behaviour of road users is an important factor in accident causati
on. Traffic psychology, defined as ''the study of the behaviour of roa
d users and the psychological processes underlying that behaviour'', a
ttempts to identify the determinants of road user behaviour with the a
im of developing effective accident countermeasures. Models of road us
er behaviour involve driver task analyses, functional control models,
and motivational models focused on risk taking and risk acceptance. Th
e relation between accident occurrence and the preceding behaviour is
largely unclear; performance aspects as well as motivational aspects,
individual differences and momentary state variables all appear to be
relevant. Attempts to modify road user behaviour involve driver traini
ng, enforcement, and rehabilitation. Given the impact of the transport
system on the environment in terms of pollution and land use, mobilit
y, and the possibilities of influencing transport mode choice and trav
el behaviour, will be a major challenge in the future.