The Contra Costa County Coroner's Office has not closed the investigation into how the 25-year-old died, but authorities said evidence indicates she jumped from the BART tracks onto southbound Interstate 680 just north of the Olympic Boulevard exit at the Highway 24 interchange.

Tracks running between the Walnut Creek and Lafayette stations run over the junction area between the freeway and highway.

Police were called to the scene about 12:15 a.m. after motorists reported a hazard in the road that might be a body, said CHP Officer John Fransen, a spokesman for the agency. Just before then, BART police were called to investigate a medical emergency on the tracks pertaining to the same person, Fransen said.

The CHP closed all lanes of southbound I-680 at Olympic Boulevard for 36 minutes after confirming the body on the freeway, Fransen said. The CHP issued a severe traffic alert at 12:34 a.m., and it remained in effect until just before 3 a.m.

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Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.