I hadn't realised that they are so long, that's over 2 miles isn't it? I usually only travelled illegally by train as a child, so that wasn't that often. The LMS was much easier to wangle than GW so it was usually out of New St for Euston rather than Snow Hill for Paddington.
I found that provided you asked first and then did as you were told, the railmen were very fair and they'd give me a mug of tea now and then - I was fascinated by trains, in part because of magnificence of a steam engine, because it was part of ''getting away'', of doing my own thing etc.
Do you use that line, or pass by Tyseley often?