Do both the two sentences below sound equally natural? For some reason, the second sentence sounds a little bit odd to me. But the grammar book I checked says that "as", "when" and "while" can be at the the beginning or at the end. So I'm just trying it out.
a) As/When/While the car was speeding down the street, it lost control and hit the pole.
b) The car lost control and hit the pole as/when/while it was speeding down the street.
Both are correct but in written English they have different meanings, because English tends to postpone the element that needs emphasis. This is a way of processing new information and is called "the principle of end focus" by Quirk, et al. To put it more simply,if you want to highlight the event in the main clause you put it after the the time clause and vice versa. The same can be true in spoken English, but in that context you can use stress and intonation to emphasise the new information.