Police have pledged to crackdown on drunken behaviour as thousands of people are expected to flock to Hull for one of Europe's largest fairs.
Hull Fair, which runs from Friday until 16 October in Walton Street, is attended by more than 750,000 people.
Humberside Police will be using a breathalyser for the first time to check if young people are drinking inside the alcohol-free zone.
Police said crime had fallen at the fair for the past two years.
Sgt Andy Parsons said: "We will not tolerate violent, disorderly or drunken behaviour that affects the enjoyment of others or those working at the fair.
"By using the alcohol tester device we will also ensure those who try to sneak alcohol on to the alcohol-free zone will be identified and dealt with."
Mr Parsons said troublemakers could be arrested or fined £80.
People attending the fair are being urged to do so on public transport.
Extra park and ride services will operate from the Humber Bridge car park and will run from 1500 BST to 2300 BST Monday to Friday and from 1200 BST to 2300 BST on Saturdays.
Hull Fair is one of the oldest fairs in the country and dates back to 1293.
It spans 16 acres at its West Park site on Walton Street.
The city's lord mayor will officially open the fair at 1700 BST.