Trains will initially only go to the platform with the waypoint. So if all trains on the line are set up to stop on every stations, and all their schedules are correctly set up so that trains in the same direction stop at the same platform, then one-way signals are not needed to avoid deadlocks. However, they are still safer, and also look better than two-way signals in this case. You can use a choose signal before the station to route a train to any free platform it can reach at the same station, but I will not recommend using them here. You might end up with a station full of trains going in on direction, and the next station full with trains heading the other direction, which is a deadlock.