I had a stop on a slight slope, as far as I know, I did my normal park and hand brake routine. I turn around after delivering, this #$%*%^$# truck is rolling back towards the right, into a yard crushing a mailbox. Its the worst nightmare dream-like experience I can't even explain. I just got reinstated after someone backed into my truck while I was out doing a delivery, now this. What I can't fathom is how we are not drilled about checking the tightness of our hand brakes every day. It should be in our diad and there should be a daily routine check by mechanics that have signatures. I've never been told anything about tightening or loosening the handbrake. We are behind these trucks countless times doing deliveries, how are we not reminded to check this every day like we are told everything else, use horns, feet on pavement, etc. I could have been killed, someone else could have been, this could have been absolutely devastating. I have some questions for a lawyer. How can the DOT not require management to regularly quiz us on handbrake checks? When we got back to the center, my sup tested the brake and it rolled in drive with the brake up. He showed me how to tighten it. Ive never been shown this. Ive never heard anyone talk about this ever.