A strike by rail workers in one of the bitter disputes over staffing and driver-only trains is being "solidly supported", causing disruption for passengers.
Members of the Rail, Maritime and Transport union (RMT) at Arriva Trains North walked out for 24 hours - the third strike in recent weeks.
The union is opposed to plans for driver-controlled operation on new trains, the issue which has also sparked strikes on Merseyrail and Southern Railway.
Arriva said it expects to run more than 40% of its normal timetable, with more than 300 additional rail replacement buses.
All services are expected to be extremely busy, with the industrial action taking place on the Friday before the bank holiday weekend and on the first day of the Tour de Yorkshire cycle event.
RMT general secretary Mick Cash said: "The RMT strike action this morning is solid as a rock right the way across the Arriva Rail North franchise as our members continue the fight to put public safety before private profit.
"If the German state-owned Arriva get away with their plans we will end up with a toxic combination of de-staffed trains and stations where safety and access are compromised while fat profits are shipped across the Channel to subsidise rail operations in Germany.
"That is a national scandal and the Government should be hanging their heads in shame.
"The public support for our members fighting for safe trains for all has been fantastic and the company should take note of what their own customers and staff are saying about their plans and sit down with the union to negotiate a safe and sustainable solution to this dispute."
Richard Allan, Northern's deputy managing director, said: "Our strong focus is on working with colleagues and customers to deliver a modern, local railway for the North that will maintain high safety standards, deliver better journeys and improve customer service.
"Our proposals, which we want to discuss further with RMT, will see staff more visible and available than ever before on trains and on stations.
"Any changes to Northern's services are always fully risk assessed, consulted upon, and approved in accordance with relevant health and safety legislation."