Diesel locomotive set, and went into series production with other streamlined car sets in Germany starting in 1935. In the USA, diesel-electric propulsion was brought to high speed mainline passenger service in late 1934, largely through the research and development efforts of General Motors from 1930–34 and advances in lightweight carbody design by the Budd Company. The economic recovery from the Second World War saw the widespread adoption of diesel locomotives in many countries. They offered greater flexibility and performance than steam locomotives, as well as substantially lower operating and maintenance costs. Diesel–hydraulic transmissions were intrdouced in the 1950s, but from the
Diesel locomotive latter are fitted low down at the front and are designed to make the locomotive easily visible as it approaches a grade crossing. Older locomotives may be fitted with a Gyralite or Mars Light instead of the ditch lights. Although diesel locomotives generally emit less sulphur dioxide, a major pollutant to the environment, and greenhouse gases than steam locomotives, they are not completely clean in that respect. Furthermore, like other diesel powered vehicles, they emit nitrogen oxides and fine particles, which are a risk to public health. In fact, in this last respect diesel locomotives may perform worse than steam