Police rushed to the A41 on Tuesday night after reports of a loose labradoodle in the carriageway.
Traffic between Hemel Hempstead and Bourne End was disrupted for half an hour before the dog was successfully detained by police with help from the public.
There were no injuries or accidents as a result of the incident and the dog was reunited with its owner.
One witness said: "We nearly collided with the dog as we were on it very quickly.
"With a car perched on our shoulder making it very difficult to avoid the dog, we were lucky not to have been involved in a collision.
"We avoided both the car and the dog thanks to the great driving of my hubby. Glad the dog is OK though."