Uncle Max is right it's not only to scare deer off that they don't cross the road, as stated by bubbles4352, the poles are sometimes placed into grassland ( i presume) and this is to scare off does to not bring their babies there.
Every year thousands of Bambies get killed by farmers when they cut the grass, because the doe leaves it lying in the meadows and goes off for the search off food, the bambi remains completely hidden in the high grass and thus gets overseen by possible predators, but not only them ( see above)......