Undercover police have been deployed on the Tyne & Wear Metro in a bid to tackle troublemakers.
Operation Hades sees plain-clothed cops and Nexus staff board trains across the network as part of an anti-social behaviour crackdown.
This follows reports of bad behaviour in North Tyneside, including youths kicking out windows and acting in what has been described as "an anti-social manner" towards passengers and staff.
Last month a train was put out of service because 10 of its windows had been kicked out.
Sergeant Tim Hand, of Northumbria Police's Metro unit, said:
The operation will run over a number of weeks and see undercover cops and Nexus staff targeting troublemakers both during the day and at night.
A Nexus spokesman said:
Anyone who sees disorder is asked to call police on 101. In an emergency, ring 999.