Two sisters were killed when their Honda Accord was broadsided by a Cook County sheriff’s squad car Thursday at a busy intersection on the border of Niles and Morton Grove.

The women were coming home after working a night shift as part of a cleaning crew at Northwestern University, family members said. They usually drove to and from work together.

The squad car was eastbound on Dempster Street at 5:47 a.m. when it hit the passenger side of the Honda, which was driving southbound on Harlem Avenue, according to Niles police. The women were pronounced dead at Lutheran General Hospital in Park Ridge after being extricated from the car by Niles firefighters.

Ludwika Moskal of Norridge, 69, was identified as the driver of the Honda and her sister, 64-year-old Helena Lukasik of Belmont Heights on the Northwest Side, was in the passenger seat.

“They were full of energy and looking forward to their retirement, which was to come in just a few months,” said Ludwika Moskal’s son, Robert Moskal.

His mother grew up in Poland and came to the United States in the 1980s, eventually settling in Norridge, where she raised her children — Robert, 44, and his 36-year-old sister. Moskal’s aunt, Helena Lukasik, had three children of her own and several grandkids.

“They were very close and did everything together,” Robert Moskal said.

The crash shut down the busy intersection for about five hours.

Niles police Cmdr. Robert Tornabene said investigators have not determined who had the green light at the intersection. Tornabene said the squad car was not on an emergency call and that its lights and siren were not activated.

“It’s just a shock right now,” Moskal said. “We’re still trying to figure out what happened.”

The officer driving the squad car, identified only as a 47-year-old man, was also taken to Lutheran General with injuries that were not believed to be life-threatening, according to police and sheriff’s spokeswoman Cara Smith. He was on duty at the time of the crash.

The North Regional Major Crimes Task Force Major Crash Assistance Team, which includes 13 north suburban departments, is investigating the crash, and the sheriff’s office was conducting an internal investigation into the crash.