MODEL:
! Traffic congestion transportation problem.
  Cost/unit increases to infinity as traffic on link
  approaches its link capacity.
  Truncated variation of an AMPL example;
SETS:
   ORIG/ CHIC CINC ERIE/: SUPPLY;
   DEST / HAM AKR COL DAY/ : DEMAND;
   OXD( ORIG, DEST): RATE, LIMIT, TRAF;
 ENDSETS
 DATA:
   SUPPLY = 1200 800 1400;
   DEMAND = 1000 1200 700 500;
   RATE =   39   14   11   14
            27    9   12    9
            24   14   17   13;
   LIMIT = 500 1000 1000 1000
           500  800  800  800
           800  600  600  600;
 ENDDATA

 [TOTCOST] MIN =
   @SUM( OXD: RATE * TRAF/( 1 - TRAF/ LIMIT));

 @FOR( ORIG( I):
    @SUM( OXD( I, J): TRAF( I, J)) = SUPPLY( I));

 @FOR( DEST( J):
    @SUM( OXD( I, J): TRAF( I, J)) = DEMAND( J));

 @FOR( OXD: @BND( 0, TRAF, LIMIT););

END