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Well, there are lots of 'introduction to highway engineering' or 'introduction to traffic management' books and books on transport policy about, but I wouldn't recommend any of those that I know, which is partly why I've been writing my own for some time. You can definitely read some of them, but if you want to gain an understanding of the issues, there's nothing better than becoming an activist. The books won't tell you that unless you then embark on a related career and gain actual experience.
On the cycling side, the best book (out of a bad field, it has to be said) is undoubtedly 'Bicycle Transportation' by John Forester, but I wouldn't recommend it, either, as it's outdated (came out in the 70s and hasn't aged well, I think), the writing style is turgid (very repetitive and rather obsessive), and it always brings people out in fisticuffs because of Forester's controversial conclusions (some of which I agree with and others of which I don't agree with). He's very good on some things, less good on others.
A good recent book, but more of a history book and not what you're looking for, is Oldenziel et al., 'Cycling Cities: The European Experience'.
@Oliver Schick - I always find these discussions fascinating; could you recommend any resources on urban (transport) design that give a good overview of the basics (textbooks? CROW manual?)?