Missing Skittish Dog: Bear, 55lb Border Collie Mix

Bear is border collie/Great Pyrenees mix, approximately 55pounds. He was hit by the mailman and bolted from our driveway. I’m not sure if he was hurt. He is skittish, please don’t chase him. He’s a rescue of 1.5 years and he’s finally acclimated to his surroundings. He hate’s loud noises and USPS trucks, FedEx trucks, anything like that. Thanks for your help.