--- a/busui/schedule_viewer.py
+++ b/busui/schedule_viewer.py
@@ -369,6 +369,7 @@
     schedule = self.server.schedule
     stop = schedule.GetStop(params.get('stop', None))
     time = int(params.get('time', 0))
+    service_period = params.get('service_period', None)
     time_trips = stop.GetStopTimeTrips(schedule)
     time_trips.sort()  # OPT: use bisect.insort to make this O(N*ln(N)) -> O(N)
     # Keep the first 15 after param 'time'.
@@ -397,8 +398,8 @@
         trip_name += route.route_long_name
       if headsign:
         trip_name += " (Direction: %s)" % headsign
-
-      result.append((time, (trip.trip_id, trip_name, trip.service_id), tp))
+      if service_period == None or trip.service_id == service_period:
+        result.append((time, (trip.trip_id, trip_name, trip.service_id), tp))
     return result
 
   def handle_GET_ttablegraph(self,params):