The annual penguin census this year was one of the lowest on record.
Trust ranger Reuben Lane said the birds were not only vulnerable to being killed by traffic, but dogs, storms, coastal erosion and coastal development.
At this time of year, they were nesting and were often out and about exploring, or looking for a mate.
"Unfortunately, some penguins choose nesting sites where penguins have nested perhaps for millennia, but a road has been developed between the nest site and the sea and, while they are feeding chicks, they will be crossing the road twice a day, putting them at great risk,'' Mr Lane said.
The trust said it hoped motorists would slow down when they saw penguin signs displayed on the roadside.
It has also been talking to Opus and the New Zealand Transport Agency about building a penguin-proof fence at the Coast Road blackspots - McCarthy Creek, south side of the Fox River bridge and Pahautane beach.
"The plan is for a simple plastic mesh fence that would prevent penguins straying on to the road at several of the major mortality sites,'' he said.