If you are suspected of doing something illegal (speeding) because your car was photographed using photo radar, I'm reasonably sure the 5th amendment applies to

If you are suspected of doing something illegal (speeding) because your car was photographed using photo radar, I'm reasonably sure the 5th amendment applies to the police or prosecutor asking you to answer any questions about that accusation. The answer could be "X person borrowed my car", which isn't, itself necessarily covered, however the answer could be "I was driving my car at that time", which is definitely covered by the 5th amendment. Since one of the possible truthful responses counts as testimony against yourself, you don't have to answer the question at all, otherwise non-answers could be seen as implicit confessions.