Work has begun to replace two century old bridges in South Canterbury, aimed at improving safety and reliability on an important inland route.

The Waihao North River and Elephant Hill Stream bridges on State Highway 82 are being removed, with construction of the replacement bridges expected to take about 12 months.

Associate Transport and South Island Minister James Meager said the condition of the two lane bridges had deteriorated to a point where replacement was more cost effective than ongoing maintenance.

Meager said the new bridges would provide safer crossings and greater certainty for people travelling on State Highway 82, which connects inland South Canterbury with destinations including the Canterbury Lakes, the Mackenzie District and Central Otago.

He said the route also provided the only convenient alternative to State Highway 1 for people travelling north and south of the Waitaki River.

Meager said the new bridges would have no load restrictions, making travel easier for freight operators and helping to improve productivity across the South Island.

Waitaki MP Miles Anderson said he welcomed the replacement of the ageing infrastructure.

Anderson said the new bridges would strengthen the resilience of the local transport network and help ensure people and goods could move safely and reliably.

The Waihao North River Bridge replacement is expected to cost $14 million, while the Elephant Hill Stream Bridge replacement is projected to cost $5.7 million, including contingencies.

Early works have already been completed, and both bridge replacements are being delivered at the same time by HEB Construction due to their close proximity.

Temporary bridges have been installed at both sites to allow traffic to continue flowing while the new bridges are built.

The two South Canterbury bridges are part of 11 structures included in the End of Life Bridge Replacement Programme run by the NZ Transport Agency, which prioritises replacement based on safety, value for money, and long term maintenance needs.