WASHINGTON (Reuters) - U.S. lawmakers on Wednesday called for an independent review of the leading auto safety regulator and a report on whether it can do more to manage product recalls and detect deadly flaws. The National Highway Traffic Safety Administration, the main watchdog for car design dangers, has come under scrutiny over its handling of recent alerts like air bags that can deploy with deadly force. "To what extent has NHTSA successfully adapted to new developments in automotive technology?" reads the request to the Government Accountability Office, an investigative arm of Congress. The bipartisan request came from six lawmakers of the U.S. House Committee on Energy and Commerce. According to the letters requesting the investigation, lawmakers want to know "why NHTSA did not act more quickly to mandate recalls before the auto companies did so voluntarily." Earlier this year, General Motors recalled more than 2 million vehicles due to faulty ignition switches, the letter said. In recent months, NHTSA has tried to manage a separate massive recall for potentially defective Takata Corp <7312.T> air bags that could spray shrapnel at occupants. (Reporting by Patrick Rucker; Editing by Richard Chang)