I don't know what they're for. I have absolutely no idea what they're for. But
I'm going to guess that maybe they're for security cameras.

maybe there's security cameras mounted inside them, and the rotation is to
allow the security cameras to see a full 360 degree view as it turns around.
and the dipoles are the radio transmitting antennas to transmit the security
cameras' pictures to the stores (or to wherever the ones on the freeways
transmit to, probably to the police station).

Once again, these are all my guesses and I have absolutely no idea what I'm
talking about here.