Default [Q] 3G in one direction but only 2G in reverse.

So I take the train every day to work and I've noticed that in the morning I usually have a solid 3G signal the whole way but on the way back I barely get 2G and browsing is practically impossible a lot if the time.

I know that signals can somewhat rubber band and be slow to hand over. However half way through my trip I stop at a station and the train sits there for about 5 min yet my phone (Nexus5) will still not attach to 3 or 4G (rebooting does not help). In the mornings going the other way I don't have this problem and always get at least a good 3G signal. What gives?