A proposal to allow bigger trucks on New Zealand highways could involve bridge upgrades costing about $85 million.
A Transport Agency report looking at the most heavily used routes found 300 bridges would need strengthening, if the plan goes ahead.
Under the Vehicle Dimensions and Mass Amendment proposal some trucks could increase their loads from 44 to 53 tonnes and logging trucks could be two metres longer.
However, the Transport Agency says the cost would be a very small proportion of the roading budget.
It says the cost would have to be weighed against savings made from heavier trucks needing to make fewer trips.