Rail bosses will be grilled by MPs on Monday over why the introduction of new timetables led to major disruption.
The Commons Transport Select Committee will question leaders from Network Rail, the government-owned company responsible for Britain's rail infrastructure, and train companies Govia Thameslink Railway (GTR) and Northern.
Hundreds of services have been cancelled or significantly delayed since schedules were changed on May 20.
Passengers using GTR and Northern have been particularly affected, with some stranded on platforms for several hours.
Both operators introduced temporary timetables on June 4, removing around 6% of daily services in a bid to boost reliability.
GTR chief executive Charles Horton announced his resignation on Friday but will still appear before the Transport Committee.
Also giving evidence are: GTR chief operating officer Nick Brown; Northern managing director David Brown and performance and planning director Rob Warnes; Network Rail managing director for the system operator Jo Kaye and route managing directors John Halsall and Martin Frobisher.
Transport Secretary Chris Grayling has blamed Network Rail for being "very late" to approve the new timetables and a delay in completing infrastructure projects.
He also criticised GTR and Northern for inadequate planning, such as not having enough drivers trained to operate new routes.
Labour MP Lilian Greenwood, chair of the Transport Committee, said passengers "are entitled to a full explanation".
She went on: "We are determined to understand how this rail timetabling chaos came about.
"What was the chain of command? If it was clear that problems existed before launch, why did it go ahead at all? Where does the blame lie? Who could have spoken up, but didn't?
"After a long period of disruption, passengers will want to know that the parties involved in this chaos are working non-stop to put things right.
"They'll want to know when services will return to normal so they can properly plan their journeys.
"Our committee will help people get the answers they deserve."
Robert Nisbet, regional director of the Rail Delivery Group, which represents the rail industry, said: "There is still more work to do to improve rail services, but the introduction of interim timetables by GTR and Northern earlier this month have had a positive impact.
"Rail employees across the country are working hard to deliver the service that customers deserve and to provide greater certainty where there is still disruption."
The session begins at 4.45pm at Portcullis House, Westminster.
The committee intends to take further evidence from the Department for Transport and others at a later date.
A separate investigation into the disruption by rail regulator the Office of Rail and Road is analysing the department's role in managing risks around major network changes, as well as the actions of train operators and Network Rail.