Book name? Post-apocalyptic fiction.?

I was telling someone about this book I read, maybe last year...cars had to pull off the road due to government intervention after some sort of global catastrophe. A family, mom, dad, 2 boys, 1 girl, in an older car, vacation maybe...was directed into a school parking lot. They parked in back, by a fence, until things got crazy and they were able to drive away. Hid in wilderness. Befriended an older couple upon whose property they were camped. The first winter was unbelievably cold. They survived by digging a shelter underground. One person died in snow. One son became a killer protecting the family. Does anyone know this book?