# Impact of Road Traffic Tendency in Europe on Fatigue Assessment of Bridges
## 1 Introduction  
Traffic-load models for road bridges given in the Eurocode EN1991-2 [1] were developed and calibrated on the basis of real traffic data, obtained in the framework of two large experimental campaigns in several European locations in the period 1980-1994 [2; 3; 4; 5; 6; 7; 8]. At that time, even though other traffic measurements were characterized by higher lorry flows, the slow-lane traffic measured in Auxerre (FR) in May 1986, on the A6 Paris-Lyon motorway, was identified as the most relevant, i.e. inducing the greatest effects on bridges. Moreover, being characterized by a high percentages of articulated lorry typologies and by low percentage of lorries with trailers, the Auxerre traffic composition was also reckoned to be well representative of the expected lorry traffic trends in continental Europe around the 2020s. For this reason, static and fatigue load models included in EN1991-2 [1] are mainly based on it. That choice has been repeatedly a posteriori validated by modern traffic measurements, carried out by more modern and accurate weighing in motion (WIM) systems and devices [5]. Of course, highly urbanized and/or industrialized areas, typically like the area served by the Boulevard Periferique in Paris (FR) or the area around the marble quarries in Carrara (IT), may be subject to even more intense traffic flow or heavier traffic composition than Auxerre traffic, but such unusual situations require specific studies, which cannot be easily generalized. It must be underlined that, aiming to improve the organization of the European transportation network, in the year 1996 the European Commission considerably modified the transport policy in the European Union, issuing the 96/53/EC Directive [8]  
The 96/53/EC Directive, amended several times, limits the total mass and length of Heavy Goods Vehicles (HGVs) to 44 t and 18.75 m, respectively, but it allows the member states to permit, following equity and non-discrimination criteria, the circulation of the so-called Long and Heavy Vehicles (LHVs). Long and Heavy Vehicles, typically employed in so-called modular transports, are characterized by total mass higher than 60 t and by total length of 25 m and more, clearly exceeding the limitations foreseen for common HGVs. To reduce transportation costs and polluting emissions, some northern European countries, in particular Sweden, Finland, The Netherlands and Germany, took the most from that possibility, so experiencing a significant increase of the number of LHVs in long-distance traffic. Furthermore, it cannot be excluded that in the near future other countries could take advantage of this opportunity, thus inducing significant changes in the long-distance traffic composition in Europe. Since LHVs were not included in the Auxerre traffic, their circulation could influence the design of new bridges and even more heavily the assessment of existing infrastructure, potentially producing a disproportionate increase of maintenance and repair costs. The consequences of allowing the circulation of LHVs is thus the subject of several recent studies [9; 10; 11; 12; 13; 14; 15; 16; 17; 18], also aiming to ascertain its potential impact in terms of fatigue damage [19; 20; 21; 22]. The study deals with the impact of LHVs on the fatigue assessment of European road bridges. With this aim, the fatigue effects produced by significant measured traffics are compared in relevant case studies. The comparison is further enriched considering the effects of fatigue load models LM2 and LM4 of EN1991-2 [1], described in Section 3. For the sake of comparison, three real traffic samples, recorded with suitable WIM devices, have been considered:  
* the slow-lane traffic in Auxerre, assumed as reference traffic;
* the slow-lane traffic measured in May 2007 in Moerdijk (NL), on the A16 Breda-Rotterdam motorway, characterized by a high percentage of LHVs;
* the slow-lane traffic recorded in March 2003 in Igualada (ES), on the A2 Madrid-Barcelona motorway.