All six southbound lanes of the highway were closed for almost two hours as the morning rush hour got underway. Two lanes re-opened shortly before 7 a.m. and the rest about an hour later.
An 8-mile traffic jam extended from DeKalb County into Gwinnett County, police said.
Investigators were trying to confirm the identities of the three dead men and to determine why they were walking across I-85.
The highway connects the Atlanta area with Montgomery, Ala., to the southwest and runs northeast to the South Carolina border.