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Salt Lake City police were trying to locate a semi-trailer rig that struck a bicyclist Thursday morning and drove away, leaving the 25-year-old woman in serious condition.

SLCPD Detective Dennis McGowan said investigators were uncertain if they the driver of the big rig intentionally fled the scene of the accident near 400 West and 300 North, or was simply unaware of the 8:30 a.m. collision.

"With these big rigs, the drivers sometimes just don't know" when they may have hit something as small and comparatively light as a bicycle, McGowan said.

The bicycle rider was initially reported to be in "very critical" condition, but she was upgraded to serious condition as of Thursday afternoon.

Anyone with information on this incident is asked to call SLCPD at 801-799-3000.

Twitter: @remims