Metro had an emergency training drill Sunday that simulated a train derailment on a bridge that crosses the Potomac River. The simulation took place on the Yellow Line. “This is one of our bigger ones [drills]because it involves the water aspect and then the District and also Virginia,” Metro General Manager Paul Wiedefeld said. He said these more complicated types of training exercises are what Metro wants. Since the train derailed while it was partly in D.C. and partly in Virginia, the drill added the extra layer of multiple jurisdictions being involved. “This is one we’re really impacting the region and we want to see how the region responds,” Metro Transit Police Chief Ron Pavlik said. Metro Transit Police, Arlington Fire Department, D.C. Fire and EMS, Alexandria Fire Department, Prince George’s County Fire Department, U.S. Park Police, U.S. Park Service and the National Transportation Safety Board were all involved in Sunday’s drill.