The total number of people transported in the first trip is 100 one way + 60 on the return trip = <<100+60=160>>160 people.
If the train made three more round trips that day carrying the same number of passengers in each trip as the first, it carried a total of 3*160 = <<3*160=480>>480 in all three round trips.
In total, the train carried 160+480 = <<160+480=640>>640 people over all its trips that day
#### 640