This paper assesses the consequences for bridges of introducing a given proportion of longer and heavier trucks, i.e. the 25.25 m and up to 60 t modular combinations so-called EMS, in a French traffic. The aggressiveness of single EMS on bridges is compared to the aggressiveness of conventional workhorses (16.5 m and 40 t). Then, some sequences of 2 EMS are compared to sequences of workhorses. Finally, the load effects induced by a real traffic flow, measured on a heavy trafficked motorway in south of France by a WIM system, are compared to the load effects induced by the same traffic flow in which some trucks are recombined into EMS, without increasing the total freight in volume or load. It is shown that EMS induce higher load effects, but remaining in the safety margin of bridges. A more critical phenomenon may be fatigue, which has still to be verified.