sentences:  While European freight trains are normally one-man operated, the larger North American freight trains are almost exclusively manned by a conductor as well as the engineer.While one-man operation is popular and on the rise among the train operating companies as it reduces the number of crew required and correspondingly reduces costs, it is for that reason controversial and is often strongly opposed by trade unions, often claiming that it is an unsafe practice.One of the first examples of a public transport vehicle that was developed specifically for one-man operation is the Birney streetcar introduced in the United States in 1916.