B-WIM is experimented in France for 15 years now, and several publications have been written about this. But generally no real attention is given to the element "bridge", that is what we try to do here. Indeed, this paper gives some elements about the issues and the structures to be chosen to carry out B-WIM tests. It also highlights the importance of the position of the sensors and the whole instrumentation system to obtain accurate results. To do this, it summarizes several B-WIM tests carried out in France by IFSTTAR (former LCPC) on reinforced concrete bridges and metal bridges. The issue of their structural behavior is addressed. Then, bridge builders and managers explain their interests in B-WIM, by reviewing the type of usual bridges in France and their health. A way to maintain their level of service needs to be found.