This paper examines the lock-in phenomenon theoretically and discusses three cases of box girders for which vortex shedding excitation was observed in the prototype bridge, and mitigation was provided by fitting guide vanes to alter the flow in the wake region. A fourth case involves a long span beam bridge for which vortex shedding excitation was mitigated through installation of tuned mass dampers. In addition, the conditions which wind tunnel tests of guide vane designs must fulfil in order to yield results which are applicable to prototype conditions have also been examined.