Kootenay Loop is a major public transit exchange in Vancouver, British Columbia. Opened on August 20, 1950, it is the eastern-most major exchange in the city of Vancouver with routes servicing East Vancouver, Downtown Vancouver, Burnaby, North Vancouver and the Tri-Cities.
Vancouver only has one public transit exchange. 
The context states the the Loop is the eastern most public transit.  By saying easternmost, it implies there is a westernmost. 
( z1 exchange :quant 1 :ARG0 ( z2 city :name ( z3 name :op "Vancouver" ) ) :ARG1 ( z4 transit :ARG1-of ( z5 public ) ) :mod ( z6 only ) )