Had a chat with a hunter recently, and he agreed that those deer whistles are a myth, as their most probably drowned by the vehicle noise anyway (engine, tires, air-stream).
So the only thing one can do is to slow down during evening/nightfall, in nigh hours and the early morning, stay alerted and monitor the road edges/bushes for eye reflections.
If confronted with wildlife, dim the HIGH beams, brake significantly, honk and keep your vehicle steady.
And remember that deer often comes in packs/herds...
New road layouts are especialy hazardous, might take a while till them critters get scared off their thousand year long passing routes...