Ken Livingstone has been elected twice as mayor

The city's mayor said delivering transport improvements would be an even bigger challenge in the next four years than in his first two terms in office.

He said some schemes were so large that any failure would lead to "huge rises in fares and business rates".

Mr Livingstone is battling for a third term in the mayoral elections on 1 May.

MAYORAL CANDIDATES Alan Craig Christian Peoples Alliance & The Christian Party Boris Johnson Conservative party Brian Paddick Liberal Democrat party Chris Prior Stop The Congestion Charge party Damian Hockney One London party Dennis Delderfield New Britain Gerard Batten UKIP Ken Livingstone Labour party Lindsey German Respect party Matt O'Connor English Democrats party Richard Barnbrook BNP Sian Berry Green party Winston McKenzie Independent

His transport plans include a �16bn cross-London Crossrail project and a �1bn per year Tube modernisation.

He also said he wanted to raise the standards of service and security on London's overground rail services, and continue improvements to the bus network.

The manifesto also includes plans for a central London bike hire scheme, involving 6,000 bicycles, with each one available for free use for the first 30 minutes and found at regular intervals on streets throughout the area.

He plans a "Veterans' Card", which would give free travel on public transport to London residents who have been injured while serving in the armed forces.

Mr Livingstone also wants to introduce a 24-hour operation of the Freedom Pass which would allow people aged 60 or over and disabled people to travel free on buses and trains all day, rather than the current system of free travel after 0900 GMT.

[Ken Livingstone's] administration has consistently fallen behind with major projects or gone way over budget, costing Londoners millions Boris Johnson Tory mayoral candidate

He said: "One of the advantages of using public transport every day myself is that I see the transport system as Londoners experience it.

"This is why throughout my life I have been committed to better public transport for Londoners, and why as mayor I have devoted so much of my time and energy to getting the transport improvements that Londoners expect."

Tory mayoral candidate Boris Johnson said: "[Ken Livingstone's] administration has consistently fallen behind with major projects or gone way over budget, costing Londoners millions.

"What kind of record is that to be proud of?"

And Liberal Democrat mayoral candidate Brian Paddick said: "What we need is a clean, fast and reliable mass transport system that can carry twice as many people as the bendy bus - London needs trams."

Green Party candidate Sian Berry said Mr Livingstone's "heart was in the right place", but added that "a Green mayor would guarantee cheaper, faster, safer travel starting with a 20p fare cut and 20mph speed limits."