Local Agricultural vehicles

It would seem that some local agricultural guys feel that the new speed limits still does not apply to them, they have no consideration toward the physical weight of the vehicle with a fully laden trailer with tyres that have the worst surface area road contact possible, brakes that are not designed for the very best stopping distance given this they contantly travel throught the village at high speed, it only a matter of time before there is a serious accident, on one occaison i raised my arm and indicated that they should slow down only for them to use a well known gesture to indicate their unwillingness to slow down, not to mention the high noise and excessive polution of over reving the engine. I notice the speed indication signs do not work any longer this might help