Experts have told the Scottish Government that the Forth road bridge is deteriorating "much less" than was previously thought, the transport minister said today.
And restricting the bridge to buses, pedestrians and cyclists would be a "huge" boost to public transport, according to Stewart Stevenson.
The minister announced yesterday that a cut-price bridge across the Forth will be at the heart of Scotland's transport strategy for the next two decades.
The new crossing would cost between 1.72 billion and 2.34 billion, compared to up to 4.2 billion in previous plans.
This, Mr Stevenson told MSPs, was because it would be narrower, as the existing bridge is to be kept open but used only for public transport.
The existing bridge has been dogged by worries that corrosion on its main cables could shorten its working life.
It had originally been feared that the bridge might have to close to heavy lorries as early as 2013 and to all vehicles at a later date.
But experts said in June said the bridge may be rusting more slowly than previously thought, and that weight restrictions might not be needed until some time between 2014 and 2020.
Today Mr Stevenson told BBC Radio Scotland: "The advice is that the deterioration is much less than we thought.
"The rate of deterioration is very largely dependent on the weight of traffic.
"When we move to a position where it's buses, pedestrians and cyclists, it's a predictable traffic flow because it's scheduled bus services, and a lower weight.
"It gives us, with the dual crossing option, much more flexibility going forward, it reduced the risk, improves the offering, and is a huge intervention in support of public transport."
Announcing the transport strategy yesterday, Mr Stevenson said the bridge would be conventionally funded.
Ministers are also to seek Treasury permission to reschedule capital spending, and if this is not granted other transport schemes may be axed in order to make the bridge a top priority.
Labour have called on the ministers to admit the "failure" of their "Scottish Futures Trust" public finance scheme.
But Mr Stevenson told Good Morning Scotland: "What always happens in times like this is that there is a flight to quality by lenders.
"And what better quality is there than investing in infrastructure backed by government?
"I expect that we will see, as the turbulence starts to ease, substantial changes in the economic opportunities."