# Impact of Road Traffic Tendency in Europe on Fatigue Assessment of Bridges
## 6 Conclusions  
In consequence of the 96/53/EC Directive, some European countries allow the circulation on their respective road networks of Long and Heavy Vehicles, characterized by length and weight going beyond the limits imposed on common Heavy Good Vehicles. The introduction of this kind of vehicles sprang from the twofold need to reduce transportation costs and pollutant emissions, but it could cause an increase of maintenance costs of existing infrastructure as well as of construction costs of new infrastructure. Considering that traffic loads on road bridges provided in EN1991-2 were defined and calibrated using the traffic recorded in Auxerre, which is very severe, but does not include LHVs, their introduction could significantly impact not only the design of new bridges, but especially the assessment of the existing ones. To discuss the consequence of circulation of Long and Heavy Vehicles on fatigue design of European bridges, the fatigue effects caused by the long-distance traffic recorded in the Netherlands (Moerdijk), characterized by a high percentage of LHVs, have been compared not only with the effects caused by Auxerre traffic but also with those produced by fatigue load models LM2 and LM4 of EN1991-2. To further corroborate the study, also actual Spanish traffic recorded in Igualada, near Barcelona, has been taken into account. Assuming the same value for the global lorry flow, the fatigue effects induced by each traffic and each fatigue load model have been compared in terms of minimum fatigue categories \(\Delta\sigma_{C,\min}\) needed to satisfy the fatigue verification or, equivalently, in terms of equivalence factors \(k_{eq}\), in this latter case making specific reference to Auxerre traffic effects. To include most of the practical cases considered in the Eurocodes, details characterized by constant amplitude fatigue limit or not have been considered, adopting, case by case, the appropriate bilinear or trilinear characteristic \(S-N\) curve. The total flow on the slow lane during the fatigue life of the bridge has been usually assumed to be \(N_{t}=10^{8}\) lorries, which is a typical value for motorways subject to intense traffic; but, for the sake of comparison, also \(N_{t}=5\times 10^{6}\) lorries has been considered, representing main roads or secondary roads subject to low intensity commercial traffic. Three important case studies have been analyzed, referring to influence lines of bending moments in simply supported and continuous beams, characterized by spans ranging in the interval 1-200 m.  
Summarizing the considerations more extensively discussed in Section 4, it can be concluded that  
* Fatigue load models LM2 and LM4 adequately reproduce the Auxerre traffic effect, generally resulting on the safe side; but, in case of details characterized by constant amplitude fatigue limit, very small spans and intense lorry flows, fatigue load models LM2, which governs fatigue assessment, can lead to results slightly on the unsafe side. * In the span range 75-200m, where simultaneity effects are important, if consecutive lorries are hypothesized belonging both to the standardized set of fatigue load model LM4, the adoption of LM4 is very much on the safe side; in fact, the probability that weights of consecutive lorries are close to the equivalent values is not important; moreover in that range fatigue assessments are often not crucial. However, if necessary, it may be opportune to use real traffic data or artificially generated traffic. * Auxerre traffic and, consequently, EN1991-2 load models cover not only Igualada traffic, but also LHV effects, as deduced from the Moerdijk traffic. Since the differences are particularly marked, this conclusion appears sound enough, even if it could require further investigations, taking into account other LHVs traffics. * Axle load distribution of Moerdijk traffic is not particularly severe, probably because the LHVs are better controlled than HGVs, thus explaining why in some cases Igualada traffic is more aggressive than Moerdijk traffic.