code: public double getTripSpeed (String trip_id, boolean straightLine) {
  
          StopTime firstStopTime = this.stop_times.ceilingEntry(Fun.t2(trip_id, null)).getValue();
          StopTime lastStopTime = this.stop_times.floorEntry(Fun.t2(trip_id, Fun.HI)).getValue();
  
          // ensure that stopTime returned matches trip id (i.e., that the trip has stoptimes)
          if (!firstStopTime.trip_id.equals(trip_id) || !lastStopTime.trip_id.equals(trip_id)) {
              return Double.NaN;
          }
  
          double distance = getTripDistance(trip_id, straightLine);
  
          // trip time (in seconds)
          int time = lastStopTime.arrival_time - firstStopTime.departure_time;
  
          return distance / time; // meters per second
      }
docs: Get trip speed in meters per second.