Without having any first-hand experience in a crash where it was needed, I can imagine many ways that it could be difficult to locate or use a knife when you are trapped.

Also, how difficult it could be to get at a trapped person and get them out, while being careful not to injure them with a knife or otherwise.

Everybody has his own preference when it comes to whether to carry a knife, what brand or type to carry, and how well they maintain it.

One suggestion would be to carry or have at hand a factory-sharp knife that is not used for anything except the emergency that you hope never happens.

Some people consider the Spyderco factory edge to be the sharpest out-of-the-box. And their serrated edges might be ideal for cutting seat belts. I haven't practiced cutting seat belts, but that would be a good idea. Also, practice breaking glass. Maybe I could find a junk yard that would let me do it.

Larry