Well, to give a nod to the advertising company.....
The point that they are (perhaps initially?) trying to drive home is...
3 feet.
3 feet.
3 feet.
Simple message.
3 feet.
That is the point they are hitting you over the head with a 2 x 4 - and in that respect, it's pretty effective.
But what does 3 feet mean?
It plainly means something to someone in a car, because the pictures are taken in a car.
It is then, that you come to the conclusion ... 3 feet....space between car and bicycle.
Would it be more effective to show a picture of a car next to a bike with "3 feet" spray painted on the car? Probably not. Folks might interpret that as - bikes keep 3 feet away from cars (not the other way around...which is the point of the board). That would just add fuel to the fire of "bikes off the road."
So, me...I'd give the ad a "B". It's a hard message to get across in one picture. "A" for effort...."C" for execution. "B" total score.