Average speed cameras have now been installed along the 20-mile stretch of roads known as the Evo Triangle.
Officials hope they will stop drivers using the roads as a race track.
Four people have been killed on the three roads since 2012.
Denbighshire and Conwy councils installed the cameras with a £500,000 grant from the Welsh Government.
The route was dubbed the “Evo Triangle” after it was made famous by motorist magazine Evo.
Supt Jane Banham, from North Wales Police, said: “We are committed to keeping people safe on the roads and our message is clear – we want people to enjoy the freedom of the road but to do so safely and responsibly.”
The cameras have been welcomed by residents and the area’s representatives in the assembly and on local authorities.
The scheme is run in partnership with North Wales Police and GoSafe, the Wales Road Casualty Reduction Partnership.
Councillor Brian Jones, Denbighshire’s leader member for transport, said: “Introducing road safety measures is only one part of the answer.
“We need people to modify their driving behaviour on our roads, to protect their own safety and that of others.”