Railroads (even publicly owned ones) are "private" property. The public doesn't have a right to access and cross the r/w. And in general it's not the RR's responsibility to provide for crossings unless they build a line that cuts something off. That said, the RRs should (especially public ones) have a defined process for somebody that wants to build such a crossing (which should not be at grade in most cases) - and they do, though often at a substantial cost. Public lines like Metrolink and Coaster sometimes do contribute to building something where there's a long-standing issue, but they don't have to.