Aérotrain faced numerous design challenges. The system would require new elevated guideways for every implementation – further pitting Aérotrain against efforts to improve existing "wheeled" rail system. Bertin's Versailles-based companies, Bertin and Co. and Aeroglide Systems, Inc., worked to resolve issues with sudden changes in air pressure, as when the train would pass another train or enter a tunnel. Prototypes used gas turbines with giant propellers, which created tremendous noise both inside and outside the train car itself – and thus required reduced speeds in urban areas. SNCF felt they already had trains that could run at those reduced speeds. Proponents pointed out electric linear induction motors could make the TACV silent. Eventually SNCF simply opposed the project, citing a broad litany of concerns.