As I have written here before ...That’s where the Russians got it right, with their broader gauge- it took the Germans quite a bit of time to re-gauge the railways as they advanced and it then spread their rolling stock even thinner.
Czar Nikolai I (1796-1855) was Czar from 1825. He took a particular personal interest in railway development in Russia, it was he who sent the first Russian engineers in 1840 to study the London & Southampton when under construction. The engineers described how "standard gauge" was being used all round Europe, you could soon take the train right across. This was the last thing the Czar wanted, who had been a junior army officer when Napoleon invaded Russia in 1812. Separate gauge and incompatible rolling stock please, not having that happen again. His engineering cleverness showed with a gauge just 4" wider, which made it it difficult/impossible with then-ubiquitous outside bearings to design adaptable dual gauge or convertible stock.
100 years on it was exactly this which considerably thwarted the German advance. There were no effective roads then either.