Chief Inspector Kevin Greenhow told ITV Border:
"The event has grown and grown and we're expecting in excess of 40,000 people over the course of the Fair. We're asking motorists throughout the North of England and South Scotland to be aware that there will be carriages and caravans on the road and they must be passed with caution.
Respect other road users and be patient. Last year was successful and safe, let's have the same again this year."
More top news
A 32-year-old man was transferred to Dumfries and Galloway Royal Infirmary for treatment, where his condition is described as stable.
The "historically significant" collection was discovered by an amateur metal-detector enthusiast on church land in Dumfries and Galloway.
Kerrie brings you Sunday night's forecast