The accident occurred around 5:30 p.m. on southbound I-95 near route 896. Police say a car and a BoltBus collided.
A woman driving a Monte Carlo was killed and her passenger, a 41-year-old man was critically injured.
Police are trying to determine why their vehicle veered across several lanes of traffic, striking the bus with 33 people on board.
Two people aboard were taken to Christiana Hospital for non-life-threatening injuries.
The victims names have not been released.