Transport bosses say improvements to the South East's road, rail and bus infrastructure are at risk from above inflation building cost rises. The South East England Regional (Seera) transport board wants the government to be more realistic about budgets.
Board chairman, councillor Nick Skellet, said building costs had risen by up to 7% but the government only allowed for a 2.25% inflation figure.
He said the funding gap hit budgets and left no money for new projects.
Seera say their figures are based on evidence from the National Audit Office and consultancy the Nicholas Group.
'Unrealistic approach'
Cllr Skellet said: "The transport board wants to ensure that the region realises its full economic potential. But that requires timely investment to keep the region moving.
"The government's unrealistic approach to construction inflation is eating away at regional investment."
Sixteen transport projects worth �530m in the South East were approved by the government two weeks ago.
Seera hopes the improvements can be brought in from 2011 to 2016.
Projects include a new rapid bus service in Brighton, Sussex, more bus links in Ashford, Kent, new platforms at Reading Station in Berkshire, and improved bus services in Berkshire, Hampshire and Oxfordshire.