create a formula to do a datediff on arrival and departure fields.

you have tio choose but you likely want to use minutes

//serviceminutes

datediff('n',table3.arrivaltime,table3.departuretime)

you can sum this formula field at the group level to get the total minutes for a route id (or use a running total if you want).

you can use that summarization (or RT) in another formula to get a persentage or a different if you want.

you can alos /60 to turn it into hours to more easily show it in comparison to total hours