The accident occurred at 10:56 a.m. in the northbound lane of on Route 252 near Hilltop Road.
Police say a Toyota Prius operated by 25-year-old Sabina Broberg of New York City was traveling south when it entered the northbound lane of travel and struck a Chrysler minivan.
Inside the minivan were 75-year-old Charles Knight and 73-year-old Mary Knight, both of the 500 block of Montgomery Avenue in Haverford. Also in the vehicle was 72-year-old Frank Szabo of Berwyn.
Charles Knight was trapped inside the crushed vehicle and had to be cut out by firefighters.
All four were transported to Paoli Memorial Trauma Center for treatment. Charles Knight is currently listed in serious condition. Mary Knight, Frank Szabo and Sabina Broberg are listed in good condition pending release.
Route 252 was closed at Hilltop Road while the accident investigation was conducted.