From what I can remember the hardest part of the job was the "split shift" system and the irregular meal times, which I'm sure affected my father's health. Also, for the conductors, was the environment inside the trams, especially upstairs where smoking was allowed, and nearly everyone smoked then

For the drivers the winter must have been hard, no heating, and they stood all the time. There weren't many routes he could have worked on, but as they changed over the years it would be difficult to list them. You could try contacting Sunderland Local Studies,
http://www.sunderland.gov.uk/index.aspx?articleid=1557 who may be able to help, but according to their site they do not hold employee records, and Tyne and Wear Archives,
http://www.twmuseums.org.uk/archives/ do have some Transport and General Workers Union records, but not employee records.
Stan