Metro riders will now be able to use their cellphones on a 1.1-stretch of the underground tunnel between Potomac Avenue and Stadium-Armory stations — the first step of a years-long process to roll out cell service from the nation’s four major carriers to the entire underground track system.

Verizon Wireless, T-Mobile, AT&T and Sprint all launched their first segment of underground cell service Thursday, Metro said Monday. Riders should now be able to communicate on that stretch of the tracks with friends and family — or emergency personnel — even if they’re a half-mile from the nearest station.

Metro’s goal is to ensure that cellphone service exists in all its underground tunnels by 2020, though they’ve said in the past that they expect many segments of the system to start offering functioning cell service long before the deadline.

With this first segment of the system completed, Metro and the four cellphone carriers now have 49.4 miles of the system to go.

“Riders have told us they want the ability to maintain wireless communication at all times while riding Metro, and this project is responsive to their needs,” Metro General Manager Paul J. Wiedefeld said in a statement Monday. “I am pleased to see the tunnel wiring project move forward under the plan I announced earlier this year.”

Metro has been criticized in the past by members of Congress and the Federal Communications Commission for the lack of functioning cell service along the tracks and in underground tunnels. Federal officials’ concerns are rooted in safety, not customer service: Cell service, they argue, could be a vital lifeline in an emergency, or if there was no way for an operator or passenger to contact Metro officials in the case of a radio breakdown.

“Quite simply, when D.C. Metro riders — often the first to see a problem developing — try to notify first responders, they frequently are unable to receive a signal strong enough to make a simple call to 9-1-1 to report the emergency,” FCC Commissioner Michael O’Rielly wrote in an Oct. 2015 letter.

Currently, there is cell phone service within all of Metro’s underground stations, as well as wireless Internet in six stations near downtown D.C.