When　traveling　by　car,　the　driver　normally　feels　that　the　return　trip　is　shorter　than　the　outbound　trip.　The　reason　for　this　feeling,　called　return　trip　effect,　is　not　clear.　To　explore　the　internal　causes　of　this　return　trip　effect,　an　indoor　driving　simulation　experiment　and　a　real　car　driving　experiment　were　performed　in　this　study.　Questionnaires　were　used　to　obtain　the　estimated　time　of　the　outbound　and　return　trips　of　the　drivers.　An　eye　tracker　and　an　electroencephalograph　equipment　were　used　to　record　driver＇s　eye　movement　and　EEG　data　in　the　real-car　driving　experiment.　The　physiological　indices　and　questionnaire　results　showed　that　the　difference　in　the　driver＇s　cognitive　loads　of　the　outbound　and　return　trips　was　the　internal　cause　of　the　return　trip　effect.　Drivers　who　were　unfamiliar　with　the　road　had　a　different　cognitive　load　between　the　two　trips,　which　resulted　in　the　return　trip　effect.　However,　drivers　who　were　familiar　with　the　road　did　not　experience　a　return　trip　effect　due　to　the　close　cognitive　loads　of　the　two　trips.　©　2020　Elsevier　Ltd