Abstract
An economic model of drivers' behaviour is introduced in order to explain recently published empirical findings telling us that road lighting increases speed, decreases concentration and reduces accidents. The model, combined with the empirical results, indicate that drivers perceive speed and concentration as complementary safety variables, while common sense suggests that speed and concentration influence real accident rate as substitutable safety means. If this holds, a positive but concave relationship between subjective and objective risks exists, which means that as the objective accident risk rises, it has less influence on perceived risk. (Author/publisher).