Preface: I have to say that this map is really compact, I have yet to be able to determine if this is good or bad; so far, good. (I like the map!)
First, for the approach to the cross-over: The cross-over and the ramp is okay, that seems to play out well. One thing I would suggest is adding some sort of window right here:
And window here would help teams see what is coming, and better prepare. Decide if they want to flank, or stay together.
The reason for this is that, when you look at the other maps, you can tell relatively early on in who's riding the cart. The exception being hightower, but hightower doesn't have a rollback ramp
THAT early into the map (Edited for clarification). The fact you do changes things. Simply adding that visibility for teams, though, will help. I don't think that having an easily flanked ramp so early in the game is an issue, it hasn't been so far in frostfell, but it is something worth paying attention to later. (that is, you can easily flank from the top or the bottom of the ramp. The trade off though is that the pushing team gets height advantage over lower-attackers, but lower attackers get the cover of the corners).
Secondly, spawns, spawn-camping and your finale: A subtle thing really. If you look at how your finale is with respect to opposing team spawn, you see that it is moving
away from the spawn, which means it is theoretically getting easier to push the cart the closer you are to the end. It should be the other way around.
As you push the cart up the hill, the pushing team gains height advantage over the mid spawn. Since mid spawn is the closest and most apparent best place to go, teams will push straight from there. Why? Because it is the quickest to get to. Downside is there there isn't a lot of cover and no quick way to height advantage. You'll see that the pushing team will have a couple people lingering there to weaken or kill anyone who leaves from there. (And just as a note, it takes 10 seconds for a heavy to run from spawnpoint, to the upper battlements through spawn. This is just a bit longer than it takes a team to push the cart up the hill)
A good example of this is hightower. You can go left, and take the first right very quickly, and be in a safe-advantageous position. The enemy team can not get up there easily, which is why you don't see a -lot- of spawn camping (It still happens, but is easily fixed because of the next point I'm about to make....). From the lower spot, you can easily access a higher spot (there is even a safe way to the higher spot). So the way those spawns are set up, you get 1) Safety 2) decent advantage and 3) Mobility to a better advantageous spot. Also, relative to the spawn doors, the final push is not moving.
You can see here, there is cover, visibility onto the point, and a clear direct route to a higher advantage.
Suggestion for fix of spawns: Make it so that you have to pass to lower spot to the higher spot in spawn, and/or add a quicker, more direct route up to the higher-level spot from spawn. Also, you could look into removing the stairs to the mid spot to prevent camping (much like hightower). Trade off is, you get a quick, straight platform to action, but when you get off, you have to take a "long" route back.
Suggestion for a fix of the finale: Make it parallel to the spawn or angle towards. (thats on you)
Ummm... I'll probably be coming back and making things more coherent, but if you have questions. You know where to find me.
EDIT: Also, signage. Resupply, battlements, arrows, etc. Even in alpha, those are really needed if they aren't clear.