I am going to guess its a mind control transmitter to make drivers come
to a complete stop rather than a rolling one. Or it might keep vagrants
from washing windshields at intersections by making them consider
getting real jobs. :-). Mike Burch K8MB

Scott en Aztlán wrote:
I've seen several of these devices attached to the street light poles
in Irvine, CA. Clearly there is some kind of radio inside the box, but
what is their purpose?

http://tinypic.com/6okknl.jpg