Prius trouble?

I love my Prius. It is the perfect car for me. Today, however, I was driving home and is was slightly snowing. Suddenly, the highway traffic was all braking and my car wouldn't stop. I pulled into the shoulder and hit the brakes. I expected to crash because I was driving fast on the shoulder in snow. But I did not lose control at all. I couldn't stop but the ABS didn't kick in and there was no fishtailing or skidding. I just couldn't stop. Eventually, the brakes kicked in and I managed to stop. But it was still very scary.