Passenger Activity Codes for advertised stops...
T = Stops to pick up and set down passengers
D = Stops to set down passengers only
U = Stops to pick up passengers only
R = Request stop
There can be up to six activity codes at each timing point. Where one of the activities is an advertised passenger stop then that should be the firstcode in the list.
N.B. Don't get the above confused with -T, -U or -D. These refer to the pick up or set down of coaches and have no bearing on the passenger activity.
At the origin location the TB, by default, will indicate an advertised passenger activity unless there is a supplementary N (non-advertised), S (staff stop) or possibly OP (other operating purposes) activity. Similarly for TF at the terminating location.