TRENTON — Suspending the Atlantic City Rail Line is necessary to make safety upgrades, NJ Transit officials told lawmakers Thursday, but they promised the shutdown was not a prelude to killing the only South Jersey train to the Shore.

The suspension, scheduled from Sept. 5 through early 2019, is being done to allow installation of Positive Train Control, a federally mandated safety system that Congress has ordered to be in place by the end of the year.

"I want to be clear: This is a temporary suspension," NJ Transit chief executive Kevin Corbett said in comments before the Senate and Assembly transportation committees. "When PTC installation is complete, we will resume full service on the Atlantic City Rail Line."

None of about 60 miles of track and none of the four locomotives or 16 train cars used on the line are equipped with PTC, which automatically controls train speeds to prevent accidents. NJ Transit is responsible for installing PTC on 326 miles of track statewide.

But the Philadelphia-Atlantic City line is the only one in New Jersey being shut down for installation. The shutdown, along with plans to shift resources from South Jersey to busier lines up north, has raised questions about why the closure is necessary.

>>READ MORE: Atlantic City train shutdown feeds fears for the future

"One thing that just doesn't hold water — no line in New Jersey nor across the country has ever been shut down to complete the system," said Nick Pittman, an area weatherman who has gained almost 4,500 signatures for a petition asking NJ Transit to reverse its decision to suspend the line. "Why is this Atlantic City line different? What work is different?"

The Federal Railroad Administration (FRA) has said it's not aware of any other railroads that  shut down service to install PTC, although railroads do not have to notify the agency to take that step. SEPTA installed PTC on all its vehicles and track without suspending any lines, though it began installing its system years ago and did not face the deadline now looming ahead of NJ Transit.

Almost 2,000 riders a day travel on the Atlantic City line. NJ Transit is directing them to use buses during the installation — an option that has not been well-received by riders.

Karen Breen-Davis of Mays Landing, and a French professor at Rowan University in Glassboro, was one of about 15 regular rail riders who traveled to Trenton by bus Thursday for the hearing. She uses the train monthly to reach appointments with a specialist at Thomas Jefferson University Hospital in Philadelphia for a thyroid condition.

"I also rely on it for seeing my grandchildren, seeing my children and family," she said. "This will change my life."

Bus service would be slower, Breen-Davis said, and she feels less comfortable with buses than the direct, predictable train service.

"We're the only rail system they're shutting down," Assemblyman Vince Mazzeo (D., Atlantic) said before the hearing. "We're from South Jersey, and we're kind of used to this — that we get knocked around a little bit."

He was seeking a compromise from NJ Transit that would allow some train service to continue while the safety system is being installed. Atlantic City has begun to rebound after the casino industry collapsed in 2014, Mazzeo said. Two new casinos opened this summer, bringing back 7,000 jobs, and pending development includes a new campus for Stockton University and a headquarters for South Jersey Gas.

"It just sends a terrible message," said Assemblywoman Patricia Egan-Jones (D., Camden).  "I just need some assurance that this is not going to drag on and on."

Because PTC installation is so far behind schedule, Corbett said, all 60 miles of the Atlantic City line must be worked on at once. In addition, NJ Transit plans to replace a portion of the track during the shutdown, he said.

NJ Transit officials don't expect to have PTC fully operational by the end of the year but hope to reach benchmarks that permit an extension until 2020. The FRA has reported that NJ Transit is at risk of failing to meet even the standard for an extension, Corbett said.

State officials said that the contractor installing PTC had done a poor job of meeting past deadlines but that a recently updated agreement included hefty penalties for delays.

The FRA has said it would not directly shut down railroads if they are not PTC-compliant in 2019, but will levy fines of up to tens of thousands of dollars a day for railroads operating without the system. Amtrak, which owns a portion of the track used by the Atlantic City Line, may also bar railroads without PTC from using its track. That would also cripple NJ Transit service around New York City.

>>READ MORE: After Philly crash, railroads got more time to install a key safety system. Three years later, some still lag behind

"If we didn't shut down the Atlantic City line, it would have shut down itself on Dec. 31," Diane Gutierrez-Scaccetti, the state's transportation commissioner, said. "It was a hard choice, and we have to make hard choices."

Legislators criticized the lack of communication over the shutdown, saying NJ Transit should have given more notification and been clearer about why the shutdown is necessary. An informational meeting is scheduled for 8 a.m. Monday at the Atlantic City rail terminal.

NJ Transit was described in the hearing Thursday as an agency in triage mode after years of neglect. While South Jersey riders are facing a loss of rail service, NJ Transit riders up north are dealing with delays, cancellations and poor communication.

The agency has 330 engineers, officials said, and needs close to 400. A minimum of 291 engineers is needed to run NJ Transit's train lines, and the shallow pool of engineers means sick days or unexpected time off can wreck train schedules. Gov. Murphy requested Thursday that the Legislature take action to waive a residency requirement for NJ Transit workers.