Local drivers are currently undertaking a 40-minute detour following the demolition of the old bridge after it was heavily damaged by rain.

Member for Cootamundra Steph Cooke said the bridge would provide temporary access to Burley Griffin Way while a permanent solution is planned and built.

"Since the rail bridge was demolished in March after it was damaged as a result of heavy rains, traffic has been detoured, adding 40 minutes to journeys and creating a major challenge for both the freight industry and local road users," Ms Cooke said.

"I want to thank everyone for their patience during this period, I regularly travel up and down the Burley Griffin Way and this detour has meant a lot more time on the road for many of us."

"This temporary road bridge over the rail line at Wallendbeen is expected to take about three months to complete. We understand the impact the closure of this bridge is having on the community and freight industry, but we're working hard to open it to traffic as soon as possible."

"The community and stakeholders will be kept up to date as the new bridge is installed."

Minister for Regional Transport and Roads Paul Toole said Transport for NSW was also working with Cootamundra-Gundagai Regional Council and Australian Rail Track Corporation to open a shorter detour route while the temporary bridge is being installed to limit the impact on motorists.

"Work to build the temporary crossing from pre-fabricated sections is expected to start in coming weeks, but in the meantime we're working on a solution to keep traffic moving because we know how important a reliable road network is to our regional communities," Mr Toole said.

"We're building a safer, stronger regional NSW, and a replacement bridge will ensure both the freight industry and local drivers are once again able to experience a more efficient and reliable journey.

"Our number one priority is the safety of all motorists and we thank the community for their patience while we investigate the best permanent solution."

Motorists are advised to drive to the conditions, plan ahead, and follow the directions of signs and traffic control.