Synonyms do not necessarily have the exact same definition (as a matter of fact, they rarely do), so it would be disingenuous to think that they are completely interchangeable. You wouldn't say "I got an excellent check-up at the doctor and then found a hundred dollar bill! What accident!" or "We were meant to be together, so it was accident that brought us together". I have had people apologize for something by saying "Sorry, it was an accident" meaning (1) they own the responsibility and (2) it was unintentional. I can't think of a time someone has called an intentional collision an "accident", and would even argue that collision softens it as "assault" would be the only appropriate word.

But I digress, collision would indeed be a more accurate word.