Delays in government backing for a new Thames crossing are damaging the UK economy, business leaders say.
In a letter to the chancellor they said delays threaten to "bring the South East to a standstill".
The Federation of Small Businesses (FSB) said the Dartford Crossing was "creaking under the pressure" of 50 million vehicles crossing each year.
The Department for Transport (DfT) said a decision on the Lower Thames Crossing would be made "in due course".
Highways England has already announced its preferred route of the Lower Thames Crossing connecting Gravesend in Kent to Tilbury in Essex.
The FSB, together with the Kent and Medway Federation of Small Businesses, the Freight Transport Association, the Port of Dover and the London Chamber of Commerce and Industry are calling on the chancellor, ahead of the budget, to guarantee the "earliest delivery" of the new crossing.
They wrote: "As our current infrastructure network stands, it threatens to bring the South East to a standstill.
"With so much of the country's international trade conducted through ports in the South East, this poor connectivity is hampering the UK economy at large."
A DfT spokesman said the government recognised a new crossing would reduce congestion and help economic growth in the South East and the UK as a whole.
He said more than 47,000 had taken part in a public consultation on the crossing.
"Views put forward in the Lower Thames Crossing consultation will inform the government's decision on the location, route and type of crossing."
An FSB spokeswoman said: "We've been hearing promises on the Lower Thames Crossing for some time now.
"The government said there would be an announcement 'in due course' but that's not really good enough.
"We're urging the government to take action now."