In the beta you could run metro ground tracks across roads, though there were some bugs associated with this. It seems they "fixed" the bugs by disallowing grade crossings entirely.
In addition, although roads can cross the mainline non-player railroads, it is not possible to lay a tram track through that crossing. This means that trams are hedged in by any railroad lines.
In addition, although roads can cross the mainline non-player railroads, it is not possible to lay a tram track through that crossing. This means that trams are hedged in by any railroad lines.