translation.en: And the reason this has not been very seriously examined before is there was a common assumption in the industry that -- well, then it might not be safe if you got whacked by a heavy car, and it would cost a lot more to make, because the only way we know how to make cars much lighter was to use expensive light metals like aluminum and magnesium.
translation.zh: 而之前没有认真研究这一点是因为 在这一行有一个不成文的假设-- 就是，如果被重车撞了，车轻了会很不安全， 这样就需要花费更高的成本 因为我们所知道的，减轻车重的唯一方法 就是使用像镁、铝这样的昂贵轻金属