Why trains were the only way to travel long distances
Trains were by far the main mode of long distance transport in Britain during World War Two. Very few families had cars, and even where they did, the driver was invariably the man of the house who was away serving in the armed forces. Petrol was rationed anyway and often unavailable for anything other than essential services. So trains were the only realistic option for relatively long distance journeys.
Overcrowding on trains
Trains were not particularly comfortable because they always seemed to be packed with army, navy and airforce personnel, often with standing room only.
Limitations on train travel
Anyway long distance journeys were a matter of necessity or special treats for families - although not of course for forces personnel. Money and resources were in short supply, and everyone felt that they shouldn't travel without good reason.
Back in the 1940s, my mother did take me with her on a 'long' journey. That was to visit her friend no further than the other side of London. Also on one occasion she took me on an even longer journey to see my father who was on leave from the army. A leave of absence from the armed forces was invariably short and often measured in hours rather than days, so my parents probably thought they would have more time together if my father didn't have to do the travelling.
Trains in the late 1940s and into the 1950s
After the war and even into the 1950s, little seemed to change on the railways. Britain was still recovering from the ravages of the war and there was hardly any spare money for investment.
Certainly I remember, in the late 1950s, my face being black with soot after travelling between London and Exeter in a train pulled by a steam engine, powered by burning coal. Of course it was my own fault for leaning out of the train window! There was always a great deal of smoke from these engines.