A dog running loose on a dual carriageway was run over and killed by traffic police on purpose because of fears it would cause a serious crash.
The North Wales force said the decision to destroy the animal was not taken "lightly" and that it had been hit at sufficient speed to ensure it did not suffer.
Several attempts had been made to catch the dog, which was running in and out of high-speed traffic and causing vehicles to swerve on the unlit A55 in the early hours of Monday.
The dog bit an officer that had tried to grab hold of it.
Chief Inspector Darren Wareing said several calls were received by the control room shortly after 3am.
He said: "The only safe option was to run the dog over at sufficient speed to ensure that it was destroyed and would not suffer.
"Other methods of destruction were considered, but were ruled out on the grounds of public safety."
Ch Insp Wareing said: "One car and an HGV had to swerve to avoid the dog whilst the officers remained on foot in the carriageway.
"The potential for a serious collision was present throughout, and in the circumstances there was no alternative way that officers could contain the dog and minimise risks to motorists."
He added: "Both officers have their own dogs and did not take this decision lightly.
"Due to the seriousness of the incident it needed bringing to a conclusion quickly for the safety of all concerned."