It happened around 10:26 a.m. off the southbound Hutchinson River Parkway near Exit 5 in Baychester.
The victim, 57-year-old George Staab, of Shirley, was pronounced dead at Jacobi Medical Center.
"A tragedy occurred earlier today here in the city," Mayor Bill de Blasio said. "A very sad report that one of our DOT electricians was struck and killed by a vehicle in the Bronx today while on the job."
Alex Bueno was out for his morning walk when he witnessed the fatal accident and called 911.
"I saw this car coming and hit the concrete corner of the bridge and flew over and fell on top of one of the workers, dragging the person down to the cliff," Bueno said.
WATCH: Witness describes fatal accident on the Hutchinson River Parkway
One of Staab's colleagues rushed to the aid of the driver.
"The DOT worker that was helping that guy, he was yelling at me, 'I can't find my partner. Look around,'" Bueno said. "Because at one point, we thought he was underneath the car."
The crash tied up traffic on the Hutch for hours - north and southbound. Area worker Darrell Powe heard the accident and said he wouldn't be surprised if speed and weather played a role in the crash.
"It was extremely foggy this morning, extremely foggy up around this end, because we are on the back bay here," he said.
Staab has been working for the Department of Transportation since 2014.
"Hard working man, this is such a sudden horrible tragedy," de Blasio said. "Just want to ask all New Yorkers to keep in your prayers, in your thoughts, keep George Staab in mind and in your heart, his family as well."
The driver remained at the scene and was treated at for minor injuries.
No criminality is suspected.
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