THE condition of an ailing bridge is forcing farmers to drive 120km to access their property on either side of the Murrumbidgee River in NSW.

Size and weight restrictions on a historic, single-lane timber truss bridge at Carrathool mean landowners with heavy vehicles or farm machinery must drive 60km west to Hay to cross the river.

They then must travel the same distance back on the other side, just to make what would otherwise be a short crossing.

The bridge, built in 1922, is listed on the NSW Heritage Register as it contains a rare Bascule lift span to allow river craft to pass.

Carrathool Shire councillor and landowner Margaret Merrylees said locals understood its historical value but needed an alternative.

"We would be very happy if the (old bridge) could be a light traffic walking bridge and they build a two-lane cement bridge alongside it that will take the traffic that needs to go over it," Mrs Merrylees said.

"We have quite a number of property owners who have land on both sides of the river and it's an absolute nightmare - and a great expense for people to go through Hay."

Mrs Merrylees said the NSW Government spent $6.5 million to restore the old bridge in 1999 and maintenance costs were high. In October, the Government allocated $11.5 million for upgrades "to provide continued safe service levels".

But Mrs Merrylees said a new bridge would make more sense. "Once they build the new bridge, the maintenance should cost less on the old bridge because it won't have the traffic," she said.