About 50 people were hurt in the underground crash in downtown Boston, though none of the injuries was life-threatening. All injured passengers that were taken to hospitals have been treated and released.
The National Transportation Security Board is investigating the crash, reports CBS station WBZ in Boston.
The Massachusetts Bay Transportation Authority already bans operators from using cell phones and recently ran an internal ad campaign featuring a poster of an open cell phone that warned employees not to drive "under the influence."
The MBTA warned drivers a year ago against text messaging or any cell phone use while they are operating a train, WBZ reports.
But general manager Daniel Grabauskas said Saturday the temptation obviously was too great for some.
"I want to remove any temptation by one or two people stupid enough to think a moment of convenience is worth the lives of the people they're transporting," he said. "I'm not going to wait for someone to die to institute a policy whose time I think has come."
Grabauskas said the new ban would apply to anyone working on board a train or bus. He said he hopes to have the policy in place within a week.
The proposal won quick support from Steve MacDougall, president and business agent of the Boston Carmen's Union, Local 589, which represents most of the MBTA's roughly 6,000 employees
MacDougall said it was clear that Friday's accident could have been "far, far worse than it was."
He said he expects some resistance to the policy from union members who believe they're being punished for the irresponsibility of a single employee. But he said he believes most workers eventually will embrace the change.
"When it comes to public safety and operating public transportation vehicles, a line has to be drawn," he said.
Watch an interview with MBTA general manager Daniel Grabauskas from CBS Station WBZ in Boston:
State Transportation Secretary James Aloisi Jr., chairman of the MBTA Board of Directors, said accidents like Friday's have become too common, citing a train accident last year in California in which 25 people were killed. An engineer involved in that crash was found to have sent and received dozens of text messages, including one sent 22 seconds before the crash.
Aloisi said he doesn't know of any policy nationwide as tough as what the MBTA is planning.
Friday's accident happened about 7:20 p.m. in a tunnel between the Green Line's Park Street and Government Center stations. A two-car train was stopped at a red signal, waiting to enter Park Station, when it was hit by another two-car train.
About 100 people were evacuated, including some who had to be extracted from the trains, and 49 were taken to area hospitals. The worst injury was a broken wrist suffered by the 24-year-old operator whom officials say admitted to police that he was sending a text message at the time of the crash.
Watch coverage of the crash from CBS Station WBZ in Boston:
While the MBTA has not released the name of the trolley driver, WBZ sources say the 24 year old is Aiden Quinn of Attleboro, a 22-month employee with the MBTA.
MacDougall said the conductor had no history of problems or complaints during his time with the MBTA. Grabauskas said the driver would be fired assuming the preliminary findings of the investigation are borne out.
"I can tell you it's difficult to contain my outrage at hearing this," Grabauskas said.
Criminal charges against the driver are being considered by the transit police and the local district attorney's office, Grabauskas said.
The Green Line remained closed Saturday as a National Transportation Safety Board team investigated the scene. Grabauskas said he hoped the line would be running by day's end Saturday.
The current MBTA policy increases penalties for workers each time they're caught using cell phones on board. Under the new one, a worker would be fired the first time he or she carried a cell phone on board. Workers have been allowed to use cell phones off the trains and buses while between trips.
Buses are equipped with global positioning systems in case the radios fail, and most trolley riders have cell phones, which could be a backup if a radio malfunctions on a train, Grabauskas said. The MBTA also has a system that allows family members to inform employees of problems at home and the MBTA to send new drivers, without using cell phones.
Grabauskas said Friday's accident leaves no doubt the change is needed.
"There's no rationale, no excuse for this," he said.