The Metrorail system on Inauguration Day will be crawling with hundreds of thousands of riders, police and officials -- including a roving medical examiner.

An employee of the D.C. Office of the Chief Medical Examiner is slated to accompany Metro's Transit Police detectives around the downtown stations Monday, just in case someone dies.

"Waiting for the medical examiner to arrive can extend the time it takes to recover service," said Metro spokesman Dan Stessel. "We are taking this extraordinary step to ensure that we are able to respond and restore service as rapidly as possible."

Train service was stopped for nearly four hours at the Ballston station after a suicide occurred earlier this month, for example, partly due to waiting for the medical examiner to arrive at the scene and investigate the death. On Inauguration Day, the agency cannot afford such delays, as crowds are thick and many riders are visitors unfamiliar with shortcuts or alternative routes to get around stoppages in the system. Road closures and security precautions could also thwart the emergency bus shuttles Metro typically uses during an extended rail outage.

Beverly Fields, chief of staff of the Office of the Chief Medical Examiner, said it is rare for staff from her office to serve in an on-call capacity for a special event. A staffer from the office also patrolled Metrorail for the 2009 inauguration, though.

She declined to provide any additional details on the unusual role for the official. "That's emergency response information, which is confidential to the city," Fields said.

In 2009, the expertise was not needed despite a close call when a woman visiting from Nashville, Tenn., fell off a crowded Gallery Place platform as a Red Line train plowed into the station. A transit police officer from Houston, helping Metro that day, helped save the woman by rolling her into a narrow crawl space under the lip of the platform.

For Obama's historic first swearing-in, the transit agency delivered a record 1.5 million trips on its buses and trains, with many trains packed to what the agency calls "crush-load" capacity.

This inauguration, fewer than half as many people are expected to attend the events, but Metro is preparing for similar crowds as a precaution. It is bringing in extra police officers to supplement its own force again, tapping 150 police officers from 15 other transit agencies around the country, from as far away as Seattle.