Seen from here, it's unbelievable how much they can to and fro over a very short line. We're not talking Trans-Siberian Railway here, for crying out loud.
In general, MY-SG crossings are made as complicated as can - with a bit of political goodwill (which is missing, obviously) they could have joint MY and SG controls at both ends of both causeways, travellers and goods having to stop only once to be processed by both countries.
Even during the Cold War years, Hungary and Austria managed to do this on their respective railways.