The man driving a regional transit bus that crashed into an house in Auburn earlier this week was on his first day of service. A Worcester Regional Transit Authority official said that Francis Artey, 27. went through a rigorous, eight-week training program before ‘‘driving in service’’ for the first time Monday. The official said Artey was an experienced school bus driver with a stellar operating record. Police say it appears that the brakes were not applied before the bus smashed into the house. They say Artey may have had a medical problem or there may have been a mechanical issue. The crash remains under investigation. Artey was hospitalized with fractures and facial lacerations, but no other serious injuries were reported.