BELGIAN ROAD TAX COMES INTO FORCE AS OF 1 APRIL 2016
From April 1, 2016, all vehicles over 3.5 tons must have an OBU in the windshield to pay road tax in Belgium
OBU stands for On Board Unit and is a box in the style of the Danish BroBizz, just about three times larger. The road tax hits both transports to and from Belgium as transit.
See more in this link:
Belgian road tax 2016