Chicago police are investigating a series of unrelated Saturday traffic crashes on the South and West sides that left at least four people dead.

The first incident occurred at about 4:17 p.m. in the 700 block of North Kedzie Avenue in Humboldt Park. Officers said they observed a vehicle speeding with three occupants strike two vehicles in traffic. Police said it first struck a minivan, and that the driver wasn’t injured.

Police said the man driving the vehicle proceeded to travel into oncoming traffic, hitting a second vehicle head-on. The driver and passenger in that vehicle were transported to the hospital, where they were treated and released, police said.

Police said the man driving the striking vehicle was transported to a hospital, where he was pronounced dead. A woman who was riding in the vehicle was also taken to a hospital but left before speaking with officers, police said. Another passenger, a man, left the scene before talking to police.

About three minutes later, a 30-year-old man hit a man with his vehicle in the 3800 block of West Madison Street in Garfield Park, police said. The man then shot the motorist multiple times, police said. He was transported to Mount Sinai Hospital where he was pronounced dead.

Later in the evening, at about 8:30 p.m., police responded to a traffic crash where a dark-colored sedan and motorcyclist collided in the 6900 block of South South Chicago Avenue in the Grand Crossing neighborhood. The driver of the vehicle, a 26-year-old woman, was traveling northbound on South Chicago when the front end of her vehicle struck the front end of a motorcyclist traveling in the same direction, police said.

Police said the woman sustained minor injuries and was transported to the University of Chicago Medical Center in good condition. Police said she was placed in custody and citations are pending. The driver of the motorcycle, a woman, was also transported to University of Chicago, where she was pronounced dead, police said.

The fourth incident happened just before midnight in the 10800 block of South Michigan Avenue in Roseland. Police said they found a vehicle that had jumped the curb and struck a building. The victim sustained trauma to the body and was transported to Advocate Christ Medical Center, where he was pronounced dead, police said.

rjohnson@chicagotribune.com