Psychological effect in tunnel group: A driving comfort study based on longitudinal spacing and brightness from expressway real vehicle test

This study identifies the critical ranges of environmental brightness difference and longitudinal spacing contributing to the psychological effect in tunnel groups. It indicates that when the brightness difference is between 500 cd·m^-2 and 2100 cd·m^-2, the psychological effect does not occur. By translating subjective driving comfort into objective parameters, this study facilitates the design of more comfortable tunnel environments, thereby improving traffic safety.