*generally* it's:
hiragana: japanese words. these are like our letters.. they mean nothing one by one but are put together to make words.
katakana: same as hiragana but used for foreign words.
kanji: these are the ones imported frm China.. each one represents a feeling or word or something like that.. i just started with the kanji >_<
anyway, that's a quick answer for ya i'll leave it to someone else to give a qualified answer...
(ie. don't put too much weight into my answers as they may be faulty.. this is ALWAYS the case with my answers
hiragana are curvy,
katakana are straight,
kanji are usually complicated and messed up.
japanese is essentially kanji broken up by hiragana particles. you can always tell the difference between chinese and japanese texts since the chinese text is all "kanji", ie a big blob of unrecognisable messed up characters.
Now with these things it often helps to translate them from the end, back.
建設中 under construction.
新宿線 Shinjuku line
中央環状 central ring (?)
高速 high speed.
首都 capital (??) OK I have no idea how that fits ... ^^;
... OK Google tells me it's 'metropolitan'
"The metropolitan high speed central ring Shinjuku line is currently under construction."
... anywhere near?
Sounds good to me. Except 高速 was actually a shortening of 高速道路, which if it had been there in its entirety I'm sure you would have translated as "expressway".
Here's an even longer one that used to appear on the Akabou trucks: