Sydney's road congestion is so bad that one third of western Sydney businesses has experienced a loss of sales, an NRMA survey says.

The survey of 451 Business Motoring Members in western Sydney found that the vehicles of more than 90 per cent of businesses faced worse traffic over the past year, while 38 per cent of business vehicles spent an extra one to three hours sitting in traffic every day.

"The economic growth of western Sydney is being strangled by congestion and the region's incredible potential won't be reached unless we can get Western Sydney out of gridlock," said NRMA President Kyle Loades.

He pointed to the importance of the construction of NSW road and rail projects, such as WestConnex, NorthConnex and the North West Rail Link.