Sutherland Shire Environment Centre has added two more electronic signs on Heathcote Road, warning motorists koalas may be crossing.
The centre can only fund the mobile variable message signs for two weeks and is seeking financial support from the community to extend the initiative.
Earlier this month, Transport for NSW (TfNSW) placed six permanent and two temporary signs between Princes Highway and Deadmans Creek.
The environment centre believes the static message are lacking and the location of some signs questionable.
A spokesman said, "We've tried to make our messages engaging, and position the signs where they will be most effective."
"The 24 kilometre stretch of Heathcote Road is notoriously dangerous for motorists and koalas alike," he said.
"Since October 22 last year, 10 koalas have been killed there - and this is only the number we know of.
"The need for more signs is needed to cover the three identified kill zones - Woronora Bridge, ANSTO precinct and Deadmans Creek.
"This short-term mitigation measure will only have the desired results if more signs are placed along Heathcote Road.
"Other measures are required while we wait for the permanent mitigation works to be completed by TfNSW at Woronora Bridge and Deadmans Creek.
Looking at speed [reduction] and even fixed speed cameras at the three identified kill zones should be seriously considered."
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