railway=;

FindMaximumFlow[railway,{1,5,6,7,9,12,13,18},{44,40}]

data=FindMaximumFlow[railway,{1,5,6,7,9,12,13,18},{44,40}, "OptimumFlowData"];

makelabels[railway_,data_]:=Block[{edgecap=EdgeCapacity/.Options[railway,EdgeCapacity]},Map[(#->Framed[Style[Row[{edgecap[[EdgeIndex[railway,#]]] ,"/",data[#]}],Directive[8.2,FontFamily->"Helvetica"]],FrameMargins->{{-.2,-.2},{-.7,-.7}},Background->GrayLevel[.9],FrameStyle->None])&,data["EdgeList"]]
];

SetProperty[data["FlowGraph"], {EdgeLabels->makelabels[railway,data]}]