diff --git a/subway_structure.py b/subway_structure.py
index 6d2307d..372dea5 100644
--- a/subway_structure.py
+++ b/subway_structure.py
@@ -1,5 +1,4 @@
 import csv
-import itertools
 import logging
 import math
 import urllib.parse
@@ -1716,18 +1715,6 @@ class City:
                 if t not in have_return:
                     self.notice('Route does not have a return direction', rel)
 
-    def validate_route_refs(self):
-        master_refs = sorted(m.ref for m in self.routes.values())
-        for ref, group in itertools.groupby(master_refs):
-            if len(list(group)) > 1:
-                # This can occur if some routes with some ref belong to
-                # a route_master, but other with the same ref doesn't.
-                self.error("Route masters {} have the same ref".format(
-                    ', '.join(
-                        m.id for m in self.routes.values() if m.ref == ref
-                    )
-                ))
-
     def validate_lines(self):
         self.found_light_lines = len(
             [x for x in self.routes.values() if x.mode != 'subway']
@@ -1794,8 +1781,6 @@ class City:
         self.count_unused_entrances()
         self.found_interchanges = len(self.transfers)
 
-        self.validate_route_refs()
-
         if self.overground:
             self.validate_overground_lines()
         else: