The Forth Road Bridge carries 24 million vehicles per year

Friends of the Earth, WWF and the National Trust for Scotland are among the 20 groups supporting a petition.

It urges the Scottish Executive to have all the facts on the condition of the existing Forth bridge before making any decision on a second crossing.

The Scottish Cabinet will discuss the issue on Wednesday.

Chairman of the ForthRight Alliance, Bill Cantley, said: "It is our belief that all options to maintain and preserve the existing bridge must be fully explored before a further new bridge is actively pursued.

'No alternative'

"Scottish ministers should have all the facts at their disposal before taking a stance on the possibility of an additional bridge. Failing to do so would be both environmentally irresponsible and fiscally imprudent."

However, Phil Flanders, director of the Road Haulage Association in Scotland, told BBC Radio's Good Morning Scotland programme that building a new bridge before HGVs are banned on the present one is key to the economy of Scotland.

If privately financed and tolled, it would cost about �7 to cross National Alliance Against Tolls spokesman

He said: "They're talking about maybe replacing the cables, nobody's tried this before on such a scale in Scotland.

"If it doesn't work and there is no alternative, then it's going to stymie the whole of the north of Scotland right up the east coast."

A spokesman for the National Alliance Against Tolls Scotland said: "A new bridge would cost about �700m. If privately financed and tolled, it would cost about �7 to cross.

"At that price no one would use it, the banks would not put up the money, and it would not be built."

Figures released last week showed that about 24m vehicles crossed the bridge last year, more than twice the load it was designed to handle.

A recent report warned the bridge could be shut to all traffic in under 14 years unless action was taken to reduce the rate of corrosion in the bridge's main support cables.

A feasibility study has been launched into fitting �12m de-humidification equipment, which would pump dry air onto the wet cables.

Proposals to charge �4 for some cars crossing during rush hour have also caused a political row.