Transport for NSW (TfNSW) says it needs to know when Anglicare will extend the Geraghty St bridge, enabling access to and from Bulli to the south.

And it said the modelling for the impact on main road intersections was inadequate.

The bridge would be "crucial" to the development.

Anglicare had permission to build an aged care facility with 80 beds along with 140 independent living units for seniors and 51 townhouses.

It is seeking to change this to 41 aged care beds and 229 independent living units, and wants it dealt with as a modification which is "substantially the same" as the earlier approval.

Consultation sessions were held late last year and government agencies have given their advice.

TfNSW said Anglicare's assessment did not properly detail the impact of increased traffic.

"The previously requested ... traffic modelling has not been provided to verify that the impacts of increased traffic at key intersections adjoining the state road network will be acceptable," TfNSW said in its advice to the major projects planning process.

"The modification does not include this analysis.

"No commitments have been made regarding the timing of the construction of Geraghty Street Bridge relative to the rest of the development.

"This is a crucial detail as it dictates where and to what extent the additional traffic will impact the state road network."

Anglicare had previously not given any indication whether the road bridge would be built before or after the housing development - leaving residents concerned about the safety of the single narrow Wrexham Rd during construction.

But an answer could be expected within "the coming weeks", Anglicare on Thursday told the Mercury.

"Anglicare Sydney continues to engage with Transport for NSW and all other development stakeholders in relation to planning approval," an Anglicare spokeswoman said.

"We will provide a response via the formal development channels in the coming weeks in relation to Modification 6 and will continue to work closely with stakeholders including the community, as the project progresses."

Transport's intervention will be welcomed by many Thirroul residents who have insisted the bridge needed to be extended before, not after, the housing development is built.

Traffic congestion in Thirroul would only worsen if scores more cars were trying to enter Lawrence Hargrave Drive via the single access point of Wrexham Rd.

The problem is a hangover from the original construciton of the housing estate there by developer Stockland. Stockland had pledged to build the bridge when it won permission for the lucrative McCauleys estate, but reneged on this commitment in 2012 after Anglicare delayed plans for the retirement village.

Anglicare encouraged people to "stay in touch via our community hotline" We encourage people to stay in touch via our community hotline (1800 965 985) or via email (community@anglicaresp.com.au).