In a long and important piece on the Stakhanovite movement, Stalin has this to say about the speed of trains. Keep in mind that the movement was part of the extraordinary and rapid transformation achieved through industrialisation and collectivisation:

We shall have in the first place, to persuade these conservative elements in industry, persuade them in a patient and comradely manner, of the progressive nature of the Stakhanov movement, and of the necessity of readjusting themselves to the Stakhanov way. And if persuasion does not help, more vigorous measures will have to be adopted. Take, for instance, the People’s Commissariat of Railways. In the central apparatus of that Commissariat, there was, until recently, a group of professors, engineers, and other experts – among them Communists – who assured everybody that a commercial speed of 13 or 14 kilometres per hour was a limit that could not be exceeded without contradicting “the science of railway operation.” This was a fairly authoritative group, who preached their views in verbal and printed form, issued instructions to the various departments of the People’s Commissariat of Railways, and, in general, were the “dictators of opinion” in the traffic departments. We, who are not experts in this sphere, basing ourselves on the suggestions of a number of practical workers on the railway, on our part assured these authoritative professors that 13 or 14 kilometres could not be the limit, and that if matters were organised in a certain way, this limit could be extended. In reply, this group, instead of heeding the voice of experience and practice, and revising their attitude to the matter, launched into a fight against the progressive elements on the railways and still further intensified the propaganda of their conservative views. Of course, we had to give these esteemed individuals a light tap on the jaw and very politely remove them from the central apparatus of the People’s Commissariat of Railways. (Applause.) And what is the result? We now have a commercial speed of 18 and 19 kilometres per hour. (Applause.)

Works, vol. 14, pp. 107-8.