Question Author
From elsewhere on the BBC site:
The National Police Chiefs' Council says it doesn't offer official guidance on how to deal with dogs on roads, and that forces and officers must decide for themselves how to react.
"It's best described as a drastic action, but possibly justified," says Doug Boulton, a former traffic officer with Staffordshire Police who runs the forensic accident investigation firm D&HB Associates. "There would have been very little time to make this decision. If cars were already swerving there might have been an accident in which a person, a child maybe, was injured or killed."
The alternatives would have been to close the road and catch the dog, or close the road, and make sure the surrounding area was clear, and shoot it. "Those would be time-consuming and there might not have been enough officers on duty in the area to block off the road in a hurry," says Boulton. "The officers wouldn't have done what they did lightly and it must have been horrendous for them to run over the dog." He adds that he's never heard of police taking this action before.
North Wales Police says other methods of destroying the dog were considered but rejected because they were too dangerous to drivers
That's a fair assessment. Shooting a stray, running dog at dark o'clock would have been difficult in the extreme. These are Police Officers with limited time and resources, not DEVGRU operatives on a search and destroy mission. It had already bitten an officer and vehicles had swerved to avoid it. They were left no option IMHO.