2 main things i noticed that were really causing backlogs, without even looking at the track layout.
1-Already mention, the full load orders. I would use full load any cargo rather than simply full load. Especially when you have 2 potential cargo's you can load on 1 train.
For passenger networks in particular i tend not to use full load orders as congestion caused by trains queuing at a station is usually more costly then trains leaving when not full sometimes.
2-You've tried to be a bit too clever with the signalling
The exit/entry system is ok for your queuing area but for actual entry to your staion it actually restricts the efficency of the station. Your much better of using path signals instead. With them up to 4 trains could be moving through that junction...2 in and 2 out, instead of ot being restricted to 1 train at all times.
With some minimal track redesign, some better orders and some better signalling the station could become much more efficient.
Part of the problem your current design has is that your trains are sitting around waiting too much which increases breakdowns which blocks the junction to your station. Using path signal also helps to prevent broken trains from totally blocking the junction. It doesn't stop it 100% but it makes it better. Personally i would turn breakdowns off as their not really very realistic.
The save is a slight redesign of the track, with 2 main issues improved. It could likely be made more efficient but that would involve a whole redesign of the track outside your station.
If you could have a look at the Central station, I haven't got anywhere to expand the station to but the queuing system may need some work 
