An American railway chief has been chosen to run London Underground but passengers have been told they should "not expect to see improvements overnight".

Tim O'Toole, 47, a lawyer from Philadelphia, has been picked by London Mayor Ken Livingstone and Transport Commissioner Bob Kiley to become managing director of the part-privatised Tube network from the spring.

He joins Mr Kiley, the former New York subway chief who heads Transport for London, at the heart of running London's transport system.

Mr Livingstone said Mr O'Toole's experience "will help turn the Underground around".

This is a system which has had a very enviable safety record long-term. These recent headlines have done something to people's confidence Tim O'Toole

But he warned: "Rehabilitating the London Underground, particularly within the confines of the government's Public Private Partnership (PPP), will be no easy task, and Londoners should not expect to see improvements overnight."

Mr O'Toole replaces Paul Godier, who was closely involved in the government's �16bn PPP deal to revamp the Tube network.

He told BBC London one of the major issues would be to restore confidence in the safety of the system.

"This is a system which has had a very enviable safety record long-term. These recent headlines have done something to people's confidence and we have to deal with that.

"The other issue is whether we can successfully move it through the PPP process without disturbance."

He was chief executive and president of the $8bn Philadelphia railway company, the Consolidated Rail Corporation, between 1998 and 2001.

'Cattle transported'

Mr Livingstone said his experience will stand him in good stead.

"He has also transported cattle," he told BBC London.

"If the Underground passengers could get the same quality of service he gave to his cattle that would be a step forward on our system."

Mr Livingstone is being given control of the Tube after abandoning his plans to take his case against the PPP to the European Court of Justice.

New team

His two-year legal battle cost the taxpayer �130m.

The �16bn, a combination of taxpayer funding, fare income and private sector finance, will be invested in the next 15 years.

Mr Kiley, who is believed to have recommended Mr O'Toole for the post, described him as "a world-class transport manager".

He will announce his management team within the next few months.