It seems to me that there are not three grammar points here, but rather one that should be named:

according to ‾ / depending on ‾

I agree with the above user - instead of having 4 separate grammar points, they really should be rolled into one, two at the most (according to/depending on, and maybe another for 'for each')

この文法ポイントは理解しにくい！ This grammar point is, in my Unicom grammar book, split into four points. Here are the constructions:

1. Noun + によって・により
2. によって(は)
3. Noun 1 + による + Noun 2
4. Noun + によると・によれば (According to)

によって ・ により shows means, cause, method, or a passive agent (手段・原因・方法・受身文の)動作主).
によっては means 「Some; for (some); certain 」(ある ‾の場合は)
Noun + による + Noun shows means and cause (手段・原因).

によっては example sentences:

明日は一日中雲が多く、ところによっては一時雨が降るでしょう。 (Unicom)
Tomorrow it's cloudy throughout the day, with intermittent rain showers in some areas.

でも、場所に よっては−−例えばアメリカの大都市… (alc.co.jp)
But in certain places, like in big cities in the United States,…

「それって、もうかるの？」「うん、人によってはね。」(alc.co.jp)
"Is it profitable?" "Yes, for some."

Here you go:

(1) 高速道路が整備されて、トラックによる輸送がさかんになった。
(2) 先週の事故は運転手の居眠り運転によるものだったことがわかった。
(3) 台風による農作物の被害が全国に広がっている。

I was wondering if someone could further explain the 3rd point or provide other examples? I tried looking it up in a grammar book I have and I asked my boyfriend, but I'm still a bit unclear.

There's a big mistake in the first point: によって・により As I can see from the examples sent by users, people are now convinced you can just replace に, in a passive sentence, with によって, nothing　could be more wrong.　My teacher has explained to me that によって can only be used if you are creating, building, discovering, writing something that was never done before or with verbs like 得る, 解明する, 発信する, 制定する, 拘束する and 運営する. によって doesn't just mean "by" and can be used instead of で when it indicates what permitted a certain developmnt of a situation (quoting my teacher: 話し合いによって解決できる。 By discussing over it we came to a conclusion). I know it is difficult to explain.

Is it always necessary to combine this with the passive verb form? A lot of the examples use the passive tense but it's not part of the usage notes, so I was just wondering!