A review of 44 of Central Otago’s bridges found 15 aging ones needed new weight limit amendments, due to changes in their structural condition.

A report commissioned for the Central Otago District Council found a further 10 bridges with no previous restrictions would also be updated with new postings, and some bridges had reduced speed limits.

A staff report with recommendations from roading asset engineer Holly Laverick and infrastructure manager Quinton Pennial was signed off by councillors last week.

Bridge postings played a vital role in maintaining road safety and protecting structures from the risks posed by overloading. 

Restrictions on heavy vehicle speed and weight limits were applied to safeguard structures that have deteriorated or were designed with lower capacities than modern General Access Limits.  

Posting a bridge involved setting a maximum weight limit per axle and/or the gross vehicle weight. In many cases, a speed limit was also enforced to reduce the dynamic effects of vehicles on the bridge, further protecting its structural integrity, the report said.

Signs were installed at each bridge approach to reflect the limits, and the chartered structural engineer carrying out the review inspected those that were either nearing the end of their life, or had structural elements that could affect performance.

From the review there were still 19 bridges that didn’t require any changes to their weight limits.

Ophir Bridge: The Daniel O’Connell suspension bridge was constructed between 1879 and 1880. The bridges speed limit was reduced in the review. PHOTO: FILE

The report identified several bridges as the only access point to properties, “and although the postings do not make the road inaccessible, they do affect how heavy vehicles use the bridges’’.

Affected parties were contacted to determine the main uses of the bridges, such as light vehicles, farm equipment and stock or fertiliser trucks, and whether alternative access was available.

The report also outlined two situations where posted bridges affected all available routes to large areas.

Strengthening works had been arranged with the aim of providing at least one route suitable for Class 1 heavy vehicles. 

“For example, the Swinburn Back Road Bridge is scheduled for pile strengthening. Once these works are completed, the bridge's posting will be reassessed.”  

Bridge 64 (Ida Valley-Omakau Road) was initially recommended to be posted but has been re-evaluated after additional supporting documentation was provided and was no longer considered necessary.

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