The dog also died, the Colorado State Patrol said.
The 39-year-old man from Tennessee was driving with a 37-year-old woman from Nevada when they had an argument, according to the Coloradoan. The woman, who was driving, stopped their Toyota on the side of Interstate 25. A dog, who was riding with them, managed to escape from the vehicle and ran onto the highway. The man ran across the road trying to save the dog when he was struck by the semitruck, according to the Denver Post.