As a preliminary study requested by the Swedish Road Administration under the project “Competitive Steel & Composite Bridges”, this report is intended to present a state-of-the-art regarding post weld treatment (PWT) implementation on bridges. Special focus is put on the High Frequency Mechanical Impact (HFMI) treatment techniques. Studies conducted at Chalmers University of Technology show that significant improvement of fatigue life can be achieved by PWT of bridge details prone to fatigue failure. This can in some cases lead to material savings with up to 28%. Fatigue enhancement procedures are today used in a variety of applications in many different industries. Some examples are crane, wind power, offshore, aircraft, spacecraft and the automotive industries. With such procedures, the automotive industry has been able to substantially reduce material consumption in their products in recent years. This has led to reduced fuel consumption, increased power output and higher safety, among other benefits. During the last seven years, PWT has become an accepted method for life extension of existing offshore structures. Thanks to the progress in understanding the performance of different treatment procedures and the development of quality assurance methods, the use of PWT techniques for fatigue life enhancement of welded details is now common practice in this field. In the bridge industry, the progress of fatigue enhancement procedures has not come as far. In many cases for steel and composite bridges, failure due to some limited number of fatigue-sensitive details is the decisive factor in design, resulting in higher material usage than otherwise necessary in ultimate or serviceability limit states. This has led to reduced competitiveness for these bridges. With implementation of fatigue enhancement methods such as PWT on a few details in steel bridges, substantial material savings can be achieved. In combination with use of high strength steel, this can result in considerable weight reduction and economic advantages. Many studies show that the fatigue strength of welded steel details can become at least 1.3-1.6 times stronger by PW-treating the weld toe, removing flaws and impurities that were introduced during welding. Moreover, the PWT also results in a smoother geometry in the transition between weld and steel plate, reducing stress concentrations. These effects together increase the number of load cycles necessary to reach fatigue failure since a high number of load cycles can be endured during the crack initiation phase. In non-treated welds, the initiation phase is negligible, thus, fatigue loading almost directly gives rise to crack propagation. The aim of this report is to give an overview of different post weld treatment techniques and set a base for further research regarding implementation of such techniques on bridges. Deeper focus is put on HFMI treatments. Mainly three questions are answered: - What international studies have been made regarding PWT, and are there relevant fatigue tests and design rules/recommendations available? - Are there examples of PWT applications in the bridge industry? - Are there any examples of FE-modeling of PWT-effects and can they give reliable predictions?