Is "as far as" the same as "to" in these sentences?
I read as far as the third chapter.
I read to the third chapter.
I'm going by train as far as London.
I'm going by train to London.
In both your cases,
I think your first examples are basically equivalent, although I would opt for the "to" version.
The second sentences I would not necessarily understand to mean the same thing. Going by train TO London indicates to me that London is a fixed destination. Perhaps you are going elsewhere afterwards, but you will getting off the train in London. Using "as far as" I don't have a very good sense of what you will be doing. Depending on context, I would either understand that to mean that you were taking the train until you got to London and then doing something else, or (conversely) that you were going no further than London on the train (and would probably get off the train before it arrived in London).
I think the first examples are equivalent because they are in the past tense, and so 'as far as' makes sense in the 'to'/'up to'/'until' context. However, the train example is discussing something which has yet to happen so its not clear that 'as far as' will in fact be 'to'.
To me there is a slight difference between: I went as far as London before turning back. (to works because I got to London) AND I'll go as far as London before turning back. (to doesn't work because I'm not necessarily going all the way to London-- it's simply the bound/maximum distance I'm willing to go).