What do the yellow boxes with a dot mean in War on the tank progress?

Solution 1:

These yellow boxes indicate the point at which the tank will be stopped by a hedgehog built by the other team. What is a hedgehog? These are those "X" shaped metal barriers that the other team builds. You can blow them up by placing an explosive charge on them.

hedgehog

The tanks will only be able to make there way to the edge of the yellow box which indicates that they have reached one of these hedgehogs. Destroy the hedgehog, and the tank will be able to advance.