Another bridge over Sydney's Hawkesbury River is being floated as part of a push to secure an expressway across the Blue Mountains.

The central west councils' lobby group, CENTROC, wants a second crossing considered as part of future upgrades to the existing Bells Line of Road.

The chairman Bill West says addressing issues of congestion east of the mountains will add momentum to the campaign for an expressway.

He said CENTROC would work with communities in the Hawkesbury and Windsor regions to look at the potential options.

"In terms of a second crossing of the Hawkesbury, it has been suggested as perhaps one of the ways that could bring this forward a little bit would be to get a second crossing to service the people in the immediate area on the eastern side of the escarpment, with the potential to link that into what will become the corridor for the Bells Line of Road," Mr West said.

The State Government has this year committed $21 million for upgrades of the Bells Line of Road.

Mr West said he wanted the government to back further development in the eastern section of the corridor.

"It would be very disappointing if the current money spent on upgrading some parts of the Bells Line of Road was all the work that was done.

"There's the demand for significant more work and that would help to upgrade the road of course, but in terms of the second crossing that is important that we have something identified so that we can actually plan it."