Yes, witnesses can be extremely important in accident cases. Without any witnesses, it would be your word against the word of the other party that caused the actual accident.
If you do have witnesses, then you have people that can support your side of the story and explain that in fact, this is what happened, and it would make your case much more strong. If there are no witnesses, it doesn’t mean you don’t have a case. You still can be a witness yourself. The circumstances that exist are also very important. One thing you should do is take pictures of the scene, if that’s at all possible. Again, it’s important to have an attorney help you with these things. They know how to investigate cases, what to look for at an accident scene, and if you have one, then they’ll probably help you to get a much better resolution.