In the [Eurometropolis Lille-Kortrijk-Tournai](https://en.wikipedia.org/wiki/Eurometropolis_Lille%E2%80%93Kortrijk%E2%80%93Tournai), there have been proposals to extend the Lille metro across the border into Belgium.  Although those proposals have been shelved for cost reasons, I wonder: does any binational metropolitan area have a mass rapid transit system extending into both countries?