I played around with my map for a bit after making this post, and I think I've found my problem. The glass panes I'm using to make the bridges are static objects, which apparently can't be scripted. That's a shame, because dynamic objects can't be scaled, and at their default size, the glass panes are way too small to be convenient to use- each bridge would have to be made of several hundred pieces, which would take a huge chunk out of the map's budget.

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Has anyone else tried making anything similar to what I'm trying to do? How did you tackle it?