In theory, only the first one is correct — it is an example of the present unreal conditional (2nd conditional). It hypothesizes about an alternate reality in the present, or an unlikely event in the future some time. Number 2, in order to be correct, should be “If the train were to HAVE CRASHED (or simply “had crashed”) at a moderate speed, there would be some passengers who WOULD HAVE SURVIVED the crash.” This is the contrary-to-fact past conditional, referring to something in the past that did NOT happen. Now, in colloquial English, native speakers often use the past subjunctive in the if-clause, even though the formal grammar requires the past perfect. What’s worse, in casual American English, “would” is often used in the if-clause: “If the train would’ve crashed…” (in both 2nd and 3rd conditionals). This is considered wrong in English, although it is perfectly correct German. You may want to check out my mini-article, which turned out to be unexpectedly popular: https://www.italki.com/discussion/164505