The collision on Indian Head Highway at Pine Drive in Prince George's County, Maryland, also injured the bus driver and another motorist; no children were aboard.
Police said the northbound Mercedes struck the bus broadside as it crossed the highway, and investigators believe the car was speeding before braking unsuccessfully.
The crash involved three vehicles at a stretch long flagged as dangerous by safety advocates, while county police and the school system conduct separate investigations.
A new national safety plan was just launched. Why do drivers still face deadly risks on a known 'Highway of Death'?
Is the 'Highway of Death' a failure of road design, driver behavior, or delayed safety technology?