The driver's union Aslef said it was "sympathetic" over the problems being faced by London Midland.
Train drivers union Aslef, however, said it was impossible to rule out further shortages in future.
Mick Rix, general secretary of Aslef, said he welcomed the intervention of the mayor.
Members of the Aslef union were to stage 24-hour walkouts on 18 January and the following Friday.
The two sides have not reached a deal, with ASLEF now drivers now declining to work extra shifts.
Train drivers' union Aslef said it agreed to the changes in rotas to "free up drivers to cover services".
BBC: London Midland timetable changes tackle driver shortage
Chief operating officer Howard Collins told BBC Radio 4 that London Underground had already met some of Aslef's concerns.
National organiser for Aslef, Simon Weller, said London Midland and some other operators had become "effectively a kindergarten" for drivers.
Later in the session, PPP was criticised by representatives from the two main rail trade unions, the RMT and ASLEF.
Members of the Aslef union have walked out for 24 hours from after voting 9-1 in favour of strike action.
Members of the Rail Maritime and Transport union and Aslef are set to walk out on 2 April and on 2 May.
Dicky Fisher from Aslef said the union would continue to work with London Midland to "assist them in delivering the train service".
BBC: London Midland timetable changes tackle driver shortage
The driver of the train, Iain Black, suffered a broken collar bone and a broken bone in his neck, his union Aslef has said.
He said the union will also talk with drivers' union Aslef.
BBC: Piccadilly Line Tube workers balloted for strike action
"The scandalous actions of the Aslef leadership are an attempt to hold Londoners to ransom, and demonstrate a wholesale disregard for our customers, " he said.
But Aslef general secretary Mick Whelan told the BBC News Channel triple pay was "not quite what we've asked for", although it had been a negotiating point.
Train drivers' union Aslef, though, suggests an alternative to closure.
Members of the train drivers' union Aslef are planning a 24-hour walkout on Sunday, claiming they should be given three extra days' pay and a day off in lieu for working the bank holiday.
London Underground drivers in the Aslef union had been considering walking out on the day of Prince William's marriage to Kate Middleton, but the threat has been removed as talks with Transport for London officials take place.
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