I noticed on the wiki that system_type == 64 can be used to indicate an underground way. I checked the pak sets I have installed, and only pak128.Britain actually makes use of this feature. It played around with building the relevant ways, all of which have way_type == wt_tram. Should they behave differently in any way than they would have if the way_type had been wt_rail? Should they behave in any way different from the way they would have if defined as tunnels?