A Dallas County sheriff's deputy was seriously injured early Saturday when he was struck and thrown off an overpass while investigating a crash on Interstate 35, authorities said.

The incident happened around 3:11 a.m. Saturday on northbound I-35, just north of Interstate 635 and over Harry Hines Boulevard, according to Doug Sisk, public information officer for the Dallas County Sheriff's Office .

Sisk said the deputy was investigating a crash when a Tesla driver became involved in a secondary collision at the same scene. The driver was detained and placed inside the deputy's patrol vehicle. Moments later, a Ford F-150 lost control on the slick roadway and slammed into the deputy's vehicle, which was parked at the crash site, authorities said.

The deputy, who was standing between

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