All underground stations on Metro will offer free wireless Internet for passengers by the end of 2018 under a new program set to launch in the summer, Metro officials announced Tuesday.

In August, Metro started a pilot program to test out a public WiFi system at six centrally located underground stations: Metro Center, Gallery Place, Judiciary Square, Union Station, Archives and L’Enfant Plaza. At the time, General Manager Paul J. Wiedefeld said the trial run would be temporary, and he would use the results to decide whether and how to expand the Internet offerings throughout the system.

Now, Wiedefeld has “greenlighted” a plan to provide publicly accessible WiFi in all underground stations, Metro spokesman Dan Stessel said.

The project would start in the summer; by the end of 2017, WiFi would be installed in 60 percent of underground stations, Stessel said. The remaining 40 percent of stations would offer publicly accessible WiFi by the end of 2018.

A detailed schedule of the WiFi installations will be released in early 2017, Stessel said.

The announcement comes amid heightened scrutiny from lawmakers and federal officials, who argue that the lack of communications infrastructure inside Metro stations and tunnels poses a significant safety risk to riders caught in an emergency situation.

As Metro officials plan for the WiFi rollout, they also continue to work with major cell providers to bring cell service to the tunnel system. Last month, they announced that Verizon Wireless, T-Mobile, AT&T and Sprint premiered underground service to the first mile-long stretch of the system, between Potomac Avenue and Stadium-Armory stations.

The entire underground system will be covered by the four major cell providers by the end of 2020.

Though the expansion of the WiFi program won’t start until the summer, riders will still be able to use existing WiFi offerings at the stations that already have it.

Originally, Metro said that the WiFi test run at six downtown stations was scheduled to last for only 45 days, after which officials said they would shut off the service to assess the results and collect public feedback.

That didn’t fly with Federal Communications Commissioner Michael O’Rielly, who sent a letter to Wiedefeld days later arguing that the pilot program was providing important safety benefits, and should not be canceled.

“I am at a loss as to why these critical communications features would be disabled at a set date. The data collected during the test period should be able to be analyzed without turning off the Wi-Fi network,” O’Rielly wrote at the time. “Given the overall questionable state of communications capabilities within the entire system, it seems counterintuitive to cease operations of an additional mechanism that the public can use to reach emergency personnel when warranted.”

Metro officials countered that all of the system’s underground stations already have cellphone service that can be used in case of an emergency. But riders have reported that service is spotty on the platforms at several stations, and that the reliability of service depends on the cell provider.