The derailment of a Red Line Metro train in downtown Washington on Monday revealed that vulnerabilities in Metro's radio communications and disaster response continue more than three years after breakdowns in those systems contributed to the L'Enfant Plaza smoke calamity that killed one person and injured scores more.

Metro said Tuesday that the broken rail was being sent to an outside laboratory for forensic testing and that it will probably be weeks before officials receive the results. The eight 7000-series rail cars — the last three of which derailed — are being inspected at the Brentwood Rail Yard in the District, the agency said.

"If you work in the transit industry, you recognize that no system is immune from the hazard of a broken rail," Metro Chief Safety Officer Pat Lavin said at a news conference Tuesday. "It is infrequent but not uncommon."

Though no one was injured in Monday's incident, some Metro board members acknowledged that they were lucky: Faulty radio communications meant it took longer for rail controllers to determine that a train had derailed, and initial reports were for smoke in the tunnel. It also took more than an hour to begin evacuating the train after the derailment, which a preliminary investigation shows resulted from a shattered rail that caused the train to slide 1,200 feet down a tunnel outside the Farragut North station.

Lavin defended the agency when asked how tracks in the area where the derailment occurred could be defective even after the year-long SafeTrack maintenance project. He pointed out that SafeTrack focused on stretches of track outside the downtown core that were older and more dilapidated.

"This was not an area that was a focus of SafeTrack. There was no SafeTrack work performed in this area," Lavin said.

The explanation was unlikely to satisfy Red Line riders, who have been subjected to repeated disruptions — including a 10-day rail segment shutdown, subsequent slowdowns from a faulty communications cable and the latest incident — since the $160 million SafeTrack program wrapped up in June.

Tuesday morning was another nightmare commute for Red Line riders as derailment repairs continued, with complaints of packed trains, overflowing platforms and waits that were significantly longer than those Metro had warned customers to expect.

Lavin said recent tests and inspections did not find any problems with track in the area of the derailment. Ultrasonic testing in August showed no internal cracks in the rail, and a specially designed vehicle that uses lasers to inspect the system also picked up no abnormalities, Lavin said.

He said that the track was visually inspected three times in January by a team of outside contractors, many of whom are retirees from the Federal Railroad Administration, and that he is confident in the quality of those inspections.

In addition, Metro planned emergency repairs Tuesday night to address the "spotty" radio coverage that prevented workers in the Rail Operations Control Center (ROCC) from immediately establishing contact with the train operator and learning that the train had derailed. Controllers initially received reports of smoke in the tunnel.

Only after repeated attempts to contact the operator and a call from another employee did ROCC staff learn that the train had come off the tracks.

Lavin said the radio signal on the side of the tracks where the derailment occurred was patchy but that the signal on the other side of the tracks has been tested and is functioning properly.

Although Metro has had chronic problems with underground radio signals throughout the system, Lavin said immediate repairs were being done only on one side of the tracks between Farragut North and Metro Center stations.

"This area is a known problem," Lavin said, when asked Tuesday why crews weren't extending their efforts to other stretches of the tunnel system. "If we have other known problems, we address those immediately, as well."

Metro blamed the smoke that was reported on the train's skid against the concrete in the narrow and dusty passageway.

After the derailment, it took 90 minutes for authorities to begin evacuating the 61 riders, train operator and a Metro Transit Police officer who had been on the train. The group was herded through the tunnel, finding their way with the aid of glow sticks.

Lavin said the lag time between the derailment and evacuation was "to ensure that the evacuation was conducted in the safest possible manner." But Metro board members were uneasy about the communication lapses and the 90-minute wait.

"In this case, we're fortunate that there wasn't any serious injury which otherwise could have led to a very tragic situation," board member Michael Goldman said. "It's the problem we had with L'Enfant Plaza — the issues of communication and coordination as well as system failures. Supposedly, we've been improving communications, and we've done drills to improve communication and coordination."

The Federal Transit Administration, which is handling safety oversight of Metro until a regional oversight body takes over, said it sent investigators to the scene "to determine what occurred" but declined to provide details, citing the ongoing investigation.

The Metro board plans a special safety meeting for Jan. 25 to address questions arising from the derailment, including why track inspectors didn't catch the defective rail, why the radios didn't work and why the evacuation took so long.

Robert Lauby, chief safety officer at the Federal Railroad Administration and chairman of the board's safety and service committee, said he's waiting for the results of Metro's preliminary investigation before deciding whether and what changes need to be made.

"Longer-term, we want to make sure we don't have other conditions that we're not aware of that could have contributed to this," Lauby said.

In response to the derailment, authorities had devised a plan to load the passengers onto a second train that would pull up from the opposite tracks. But about an hour after the derailment, the plan was abruptly scrapped. D.C. Fire and EMS Chief Gregory Dean said Tuesday that concerns about the tight squeeze, and reactivating third rail power in a space where 63 people would be crammed, prompted the alternative plan.

"There was not a need to quickly do anything," Dean said. "So the initial plan was that it's dark in there, it's uneven walking, so if we can get a rescue train in, let's try a rescue train. . . . In the process of doing that, they decided, 'Hey, this is not [going to] work because of how much room the train itself takes up.' "

Metro received word of the incident at 6:28 a.m., and the Office of Unified Communications was called at 6:35, according to Fire and EMS records. From there, crews were dispatched at 6:40 a.m. and arrived at 6:43 a.m. — 15 minutes after the derailment.

Metro's last passenger service derailment took place in July 2016, when deteriorating wooden ties failed to secure the position of the two steel rails over time. The derailment led Metro to terminate one-third of its track inspection department after an investigation determined that workers and managers falsified inspection reports and failed to perform routine visual surveys of all of the tracks.

Radio signal and tunnel communication issues in the system's downtown core have been a persistent issue. During the January 2015 L'Enfant Plaza smoke calamity, the lack of an underground radio signal was a major factor in the significant miscommunication between Metro staff and the fire department — and one of the reasons why it took more than 30 minutes to get passengers off a train filling with smoke.

In December, in response to an FTA requirement that it update federal officials on systemwide radio quality, Metro said it "developed procedures for monitoring radio coverage and performance" and identified areas for improvement.

Metro said Farragut North was not among them. The agency is in the beginning stages of a replacement of its entire radio communications system — throughout its tunnel, track and bus network — using upgraded technology that will automatically alert staff if the radio signal is weak. The $160-million project has been awarded to Motorola Solutions and is scheduled to be completed in 2022.