Highland Council has estimated that the gross total cost of replacing all its road structures, if it ever had to, would run to more than £650m.
The local authority is responsible for about 2,200 bridges and culverts and more than 1,000 walls on its 4,195 miles (6,752km).
It has the most road structures and the longest road network of Scotland's 32 local authorities.
It is having to spend £350,000 on improvements to four bridges.
They are Struy, Achfary, Blackburn and Coronation.
Community services committee chairman Allan Henderson said: "We have a huge number of bridges across our road network in the Highlands and many of these are vital to connect local communities, particularly in rural areas.
The council continually has to prioritise where limited resources can be allocated to carry out essential repairs.
He added: "Recognising the importance of our roads across the Highlands, it is our intention to propose a significant programme of investment in our roads and bridges for agreement at council in December."
