A 20-year-old woman died after she fell from a Mercer Island overpass near Island Crest Way onto the east-bound Interstate 90 express lanes on Thursday evening.

Washington State Patrol Trooper Rick Johnson Tweeted that the woman was not struck by vehicles and was transported to Harborview Medical Center, where she died of her injuries shortly after.

It is unknown if the woman’s fall was accidental.

The I-90 express lanes were closed for several hours during the investigation.