T-SQL: Calculate Hours, Mins and Secs from StartTime and EndTime

select  
  sum(TotalSeconds) / 3600 as Hours,  
  (sum(TotalSeconds) % 3600) / 60 as Minutes,  
  sum(TotalSeconds) % 60 as Seconds  
from  
(  
select ArrivalTime, DepartureTime, DateDiff(second, ArrivalTime, DepartureTime) as TotalSeconds  
from SSR  
where CustomerID = 10  
) x

Thanks to this site for the heads up.