The Palm Beach County Sheriff's Office wants to hear from anyone who may have witnessed a shooting on I-95 in Boynton Beach around 12:30 p.m. Monday.
Deputies were called to the southbound lanes where four people in a Lexus were shot by someone in another vehicle, which sped off.
The victims drove themselves to the hospital where one man was pronounced dead on arrival.
The other adults are being treated for their injuries, but expected to survive.
Authorities say they are not cooperating with the investigation.
Witnesses are asked to call Palm Beach County Crimestoppers at 1-800-458-TIPS.