My car will suddenly shut off while driving, lights still on.

What is your question?

Never had a problem before. Oil was changed a month ago, doesn't overheat or anything, just stops. The power steering goes out, but the radio and lights still work. I've had it looked at twice but it happens so sporadically that they haven't been able to diagnose it. HELP! I'm starting to become terrified of driving this car in case I cause an accident for it shutting off in heavy traffic. Thank you!