set INTER;  

param entr symbolic in INTER;          
param exit symbolic in INTER, <> entr; 

set ROADS within (INTER diff {exit}) cross (INTER diff {entr});

param cap {ROADS} >= 0;  

node Intersection {INTER};

arc Traff_In >= 0, to Intersection[entr];
arc Traff_Out >= 0, from Intersection[exit];

arc Traff {(i,j) in ROADS} >= 0, <= cap[i,j],
   from Intersection[i], to Intersection[j];

maximize Entering_Traff: Traff_In;