Parallel Transmission Lines

I am studying the RTS 96 test system for a power system simulation in Matlab. I have noticed that under the Branch Data file, there are some buses which have two lines connecting them. For example (from Table-12.txt) between buses 115 and 121

ID#       =  Branch identifier.
Inter area branches are indicated by double letter ID.
Circuits on a common tower have hyphenated ID#.
Lam-p     =  Permanent Outage Rate (outages/year).
Dur       =  Permanent Outage Duration (Hours).
Lam-t     =  Transient Outage Rate (outages/year).
Con       =  Continuous rating.
LTE       =  Long-time emergency rating (24 hour).
STE       =  Short-time emergency rating (15 minute).
Tr        =  Transformer off-nominal ratio.
Transformer branches are indicated by Tr <> 0.

ID  From  To  L -  Perm.     Tran.   R     X     B   Con LTE STE Tr
#    Bus Bus miles Lam-p Dur Lam-t   pu    pu    pu  MVA MVA MVA pu
A25-1 115 121  34   .41    11  0.8  0.006 0.049 0.103 500 600 625 0
A25-2 115 121  34   .41    11  0.8  0.006 0.049 0.103 500 600 625 0


Is the reason purely physical, meaning, introducing redundancy to increase system security? When it comes to modeling, can I just combine these into one transmission line (with appropriately modified parameters)?