code: def get_tripIs_active_in_range(self, start, end):
          
          to_select = "trip_I, day_start_ut, start_time_ut, end_time_ut, shape_id "
          query = "SELECT " + to_select + \
                  "FROM day_trips " \
                  "WHERE " \
                  "(end_time_ut > {start_ut} AND start_time_ut < {end_ut})".format(start_ut=start, end_ut=end)
          return pd.read_sql_query(query, self.conn)
docs: Obtain from the (standard) GTFS database, list of trip_IDs (and other trip_related info)
          that are active between given 'start' and 'end' times.
  
          The start time of a trip is determined by the departure time at the last stop of the trip.
          The end time of a trip is determined by the arrival time at the last stop of the trip.
  
          Parameters
          ----------
          start, end : int
              the start and end of the time interval in unix time seconds
  
          Returns
          -------
          active_trips : pandas.DataFrame with columns
              trip_I, day_start_ut, start_time_ut, end_time_ut, shape_id