--- a/python/moving.py	Tue Jul 08 16:59:35 2014 -0400
+++ b/python/moving.py	Tue Jul 08 17:04:55 2014 -0400
@@ -637,7 +637,7 @@
     def __init__(self, S = None, Y = None, lanes = None):
         if S == None or Y == None or len(S) != len(Y):
             self.positions = [[],[]]
-            if len(S) != len(Y):
+            if S != None and Y != None and len(S) != len(Y):
                 print("S and Y coordinates of different lengths\nInitializing to empty lists")
         else:
             self.positions = [S,Y]