Answer:
Robert Black is an Abnegation born member who later transferred to Amity. Robert was born in the Abnegation faction with his sister, Susan, and are neighbors of the Priors. Their father works around the city, traveling around in his car, so he drives the siblings to and from school everyday. He occasionally offers to drive the Prior siblings as well, but they courteously turned down his offer, being the Abnegation children they are who would not want to inconvenience anyone.