Metro has purchased 26 new mobile emergency response vehicles. Image courtesy WMATA. WMATA has purchased 26 new light-weight, battery operated carts to help ferry first responders to subway accidents and evacuate passengers from danger. The transit agency unveiled the vehicles on Wednesday. The mobile emergency response vehicles (MERVs) move along the rail tracks, are powered by an electric motor and can be assembled quickly by emergency crews. Their big advantage is speed: Metro says…