The role of traffic psychology in psychopharmacological research

• The ecological relevance of psychopharmacological literature is enhanced by real driving studies.
• Traffic psychology has a firm place in traffic and transport research and development.
• Traffic psychology is acknowledged as an important human factors issue.

After the definite breakthrough of the awakening to the negative effects of alcohol on traffic safety, some 50 years ago in the sixties of the past century (see Borkenstein et al., 1974), authorities began to worry about drugs, initially medicinal drugs. After World War II, the prescription and administration of medicinal drugs expanded enormously. Pharmaceutical research was booming, for instance leading to the extremely successful introduction of Benzodiazepines, a group of depressing drugs administered for various symptoms. Laboratory studies gave strong indications that at least some medicinal drugs were likely to affect traffic safety. However, contrary to alcohol, no unambiguous effect with respect to traffic safety could be assessed easily by standard methodology, i.e. epidemiological research. Thereupon a new line of experimental research was developed, in the field itself, by means of instrumented vehicles. People were administered medicinal drugs, and placebo in double-blind within-subjects cross-over designs, driving on closed circuits or in some countries even out on the public road under strict surveillance. Several performance measures were registered, of which “swerving” or “weaving”, i.e. the control over lateral position as measured by the standard deviation of lateral position (SDLP) came forth as the most promising. To date SDLP proved itself as the most valid and reliable indicator of performance deterioration, and is at the basis of recently developed categorization systems of (medicinal) drugs.