KINGSBRIDGE - Transit union officials are coming to the defense of bus drivers across the city after a Bronx driver was assaulted by a passenger who refused to pay. Authorities say Nelson Diaz, a veteran driver on the Bx41 route, was attacked while parked at a bus stop at East 162nd Street and Melrose Avenue. They say a man who did not want to pay his fare started hitting him. Union heads say police need to boost their presence at bus stops and the MTA needs to erect more barriers on buses. They claim the Bx41 line is the second most dangerous in the city, and that bus driver attacks are up 2 percent from 2011. An emergency crew took Diaz, 53, to Saint Barnabas Hospital, where he is being treated for a concussion. No arrests have been made.