I saw in the demand modeling that borders are (generally) considered to be "hard" (at least, in the model example given, which used Helsinki and the Finnish/Estonian sea border). Given the presence of a body of water there, I was wondering if the same thing applied on all-land borders. In particular, I was wondering if the same thing applied with (for example) the US/Canadian border (or the US/Mexican border) since IIRC Bellingham (Vancouver) and Detroit (Windsor) generate a modest stream of traffic from large metros across the border (partly due to nosebleed prices in Canada). I think Burlington does the same (Montreal), and I can imagine that San Diego or El Paso also generate some cross-border traffic.
I'm trying to think of obvious (non-EU/EEC/EFTA-related) cases elsewhere in the world...potentially setting aside Singapore and Hong Kong as special cases (is Hong Kong a "country", for example) and I'm coming up a little short.
The border crossing rules are not fully activated yet, so most of them are still closed (even land borders of "friendly" states). The data is added in small increments.