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Motorists could face tolls of $3 on roads built under a National government, National Party transport spokesman Maurice Williamson said today.

In August, Mr Williamson got into trouble for saying people would be happy to pay $5 each way on a toll road - which equated to $50 a working week.

National's leader, John Key, described the MP as "excitable" and said tolls were more likely to be around $2.

On Radio Live today, Mr Williamson added a dollar.

"Of course the answer to that is it depends on which road," he said.

"If it is quite a short distance road of a few kilometres, somewhere in the city-type link, you'd only be talking of $1 or $2. If it's a very long haul road you may be talking of $3.

"Those are the sorts of numbers."

Mr Williamson said legislation ensured there were free alternative roads.

He said there may be cases where that was impossible but he did not know of one.