Rear-end　crashes　are　one　of　the　most　common　crash　types.　Passenger　cars　involved　in　rear-end　crashes　frequently　produce　severe　outcomes.　However,　no　study　investigated　the　differences　in　the　injury　severity　of　occupant　groups　when　cars　are　involved　as　following　and　leading　vehicles　in　rear-end　crashes.　Therefore,　the　focus　of　this　investigation　is　to　compare　the　key　factors　affecting　the　injury　severity　between　the　front-　and　rear-car　occupant　groups　in　rear-end　crashes.　First,　data　is　extracted　from　the　Fatality　Analysis　Reporting　System　(FARS)　for　two　types　of　rear-end　crashes,　including　passenger　cars　as　rear-end　and　rear-ended　vehicles.　Significant　injury　severity　difference　between　front-　and　rear-car　occupant　groups　is　found　by　conducting　likelihood　ratio　test.　Moreover,　the　front-　and　rear-car　occupant　groups　are　modeled　by　the　correlated　random　parameter　logit　model　with　heterogeneity　in　means　(CRPLHM)　and　the　random　parameter　logit　model　with　heterogeneity　in　means　(RPLHM),　respectively.　This　study　provides　an　insightful　knowledge　of　mechanism　of　occupant　injury　severity　in　rear-end　crashes.