A 39-year-old Tennessee man is dead Sunday evening along Interstate 25 near Fort Collins after getting hit by a semi-truck while trying - but failing - to save his dog who'd gotten out of the car, state troopers say.

Colorado State Patrol says at 5:33 p.m., a couple stopped on the side of I-25 to argue - that's when the man's dog escaped the car.

The man tried to save the dog, but he was hit and killed by a passing semi. The semi stayed at the scene, authorities say.

I-25 northbound is down to one lane at Harmony Road due to the crash with no estimated time of a full reopening.

It's not known yet if the dog was also hit by the semi or another passing vehicle, CSP says.

No word on if the driver will be charged.

CSP is asking any witnesses of the crash to call the CSP tipline, *CSP (*277).