what are purple boxes by highway?

Last month driving on an interstate I became aware of dark purple boxes, aprx. 18" high by 6" wide, hanging along the edge of the road.  They are hanging too high to be something bored teens did.  I noticed them about every 3 miles in one area.

Now I've seen one on another road.  Today, on the interstate that I drive everyday, I noticed there is one and I was sort of expecting to see one, as they are everywhere else.

What do they represent?

They are insect traps for the emerald ash borers. I guess they are getting into the trees and killing them.

aha.  I wondered about that but thought they were too pretty.  But no reason a trap has to be drab. 

Against the dark green foliage, they aren't that conspicuous.

Traffic and shoulder of road didn't allow me to pull off safely to investigate.

The bugs are probably attracted to that particular colour...

I think these boxes have nothing to do with bugs but, rather are a deer warning.  The holes would help the wind make noise to deter deer from coming too close the road.  But emerald ash borers could be the case.  I have seen the boxese in New York, Pennsylvania and Ohio - normally on roads traveling North and South as opposed to East and West.