Budd–Michelin rubber-tired rail cars remained obscure in comparison with other competitors for the title, such as the "Pioneer Zephyr" and Union Pacific's M-10000. Rubber-tired rail cars achieved greater success in France, and similar rubber-tired subway cars have been adopted in Canada and Mexico as well as on numerous systems in Europe. During the 1920s, the American Budd Company, at the time a relatively obscure auto-frame supplier, developed an extensive working relationship with the French firm Michelin, which was best known for its tires. In 1929, Michelin built its first rail car, and by 1932 nine of its cars were in operating service, all of
International Rubber Regulation Agreement by lack of knowledge of the chemical structure of rubber compounds until after 1945. DuPont had developed neoprene in the 1920s in response to the Stevenson Plan, but neoprene was too costly for making tires. During this period the International Rubber Research & Development Board and the Research Association of British Rubber Manufacturers were founded. Also other technologically advanced countries like Germany and the Soviet Union developed in the interwar period synthetic rubber (e.g. Buna. But this was always more expensive than natural rubber. The first and only agreement to come from the United Nations Conference on Trade and Development