There have been a number of catastrophic train crashes in recent years that may seem to have been isolated incidents. But, it turns out, they are connected in an important way. They illustrate a failure in the railroad industry to implement a life-saving technology that could have prevented them.

The list of accidents includes one last year in Cayce, South Carolina where an improperly aligned track switch sent Amtrak's Silver Star, its crew and more than 100 passengers careening off the mainline track and barreling into a CSX freight train parked on a siding.

Emergency responders are at scene after Amtrak train collided with freight train and derailed near Cayce, South Carolina, on February 4, 2018 Randall Hill / REUTERS

Mark James: When it hit, I mean, you can couple up at six miles an hour, and it'll shake the ground. And this thing hit at 51 miles an hour. And the blast was unbelievable.

Mark James was right there. He was the engineer of the CSX freight train that night.

Mark James: And they're bringing people off with broke arms, legs, people fr-- mangled really. And this is something I'll never, I'll never get over. I couldn't imagine anybody else that's ever seen that before.

Lesley Stahl: And right up close.

Mark James: Yeah. That close.

As the engineer, Mark James was driving the CSX train along different tracks in the yard, in order to unload freight.

That night he and his conductor were working under unfamiliar conditions because the electrical signal system - that sends out alerts when the tracks are not lined up properly - was out of service.

Mark James: Nobody can see what we're doing. It's called dark territory.

It was the CSX conductor's job that night to throw the switches by hand like this to realign the tracks and thereby change the direction the train could go.

Lesley Stahl: Are there a lotta switches?

Mark James: Lotsa switches, yes.

Lesley Stahl: Like, how many?

Mark James: He probably handled close to 40 switches that evening.

Mark James

But there was only one switch that would matter for the passengers and crew of Amtrak's Silver Star, the switch to keep Amtrak on the main line.

Mark James: That's when I ask him, "Did you get the mainline switch?" And he assured me that he had thrown it 100 percent.

Lesley Stahl: He said, "100 percent?"

Mark James: Uh-huh.

Lesley Stahl: In the training, does it say that you-- you should check, you should double-check?

Mark James: No. There's no way I can get off a locomotive and go check every switch he throws. That way, you'd get nothing done.

Lesley Stahl: But you had a feeling.

Mark James: Yeah. I did. I asked him multiple times. I trusted him that he had gotten the switch back.

At that moment, southbound Amtrak 91 was bearing down on that mainline switch that would send it into the CSX freight train. Mark James says he had gotten off the train to stretch his legs.

Mark James: I get down and I'm expecting these headlights very bright coming to get on past us. And then I see-- you could tell when that train hit the-- hit the switch and came in on top of us, you could see where it-- where it rocked., my mind was just crazy. I didn't-- "Oh, my God, no. Please no. Please no."

A surveillance camera near the tracks captured the Amtrak train as it went under a bridge and slammed into the stationary CSX train.

Mark James: And it was just tearing the locomotives up. And it went up over and turned over that way. And there was nothing left of where I was sitting. And I thought my conductor was dead.

Lesley Stahl: Was he sitting right at the point of impact?

Mark James: As the collision was happening, somehow he made it out the back door. So I'm talking to him. He's in shock. He's sitting there saying, "I know I got that switch back. I know I got that switch back--"

This is what was left of the other train's locomotive. That Amtrak train's engineer and conductor were killed. One of the passenger cars folded in half. More than 90 people were injured.

Robert Sumwalt: It only took about seven seconds from the time that it hit this switch--

Lesley Stahl: Oh.

Robert Sumwalt: And it collides with the stationary CSX.

Robert Sumwalt

Robert Sumwalt is the chairman of the National Transportation Safety Board, which is investigating the crash.

Lesley Stahl: What if that CSX train had toxic chemicals in it?

Robert Sumwalt: Well, we've certainly seen accidents with toxic chemicals onboard, where a switch was left in the wrong position right here in South Carolina, in fact.

It was just over 50 miles away, in Graniteville, where a Norfolk Southern freight train derailed in 2005, leaking tons of chlorine gas, killing nine people and leaving 554 with respiratory injuries.

Lesley Stahl: And the town has never been the same, as I understand it.

Robert Sumwalt: Well, that's right. So people might be thinking, "Well, I-- this-- I don't care about this story. I don't ride a train." But most communities have railroad traffic going through it.

Albert Linden: Every day you get some of the locomotives loaded with everything. They heading that way, and they moving 60 miles an hour, too.

Albert Linden owns an electrical contracting business next to the crash site in Cayce, South Carolina. It was his surveillance camera that captured the accident.

Albert Linden: These tracks are in horrible shape.

Lesley Stahl: Had you ever seen any other accident? Any derailment?

Albert Linden: Yes, ma'am. It's quite frequent.

Lesley Stahl: It's frequent?

Albert Linden: In the last ten years, there's probably been seven, eight of them. They forgot to flip the switch, and derailed them in here.

Lesley Stahl: The same thing?

Albert Linden: Yes, ma'am. Forgetting to flip the switch.

Lesley Stahl: And you're just sitting here, watching this unfold before your very eyes?

Albert Linden: They, they-- it's a common occurrence.

But those didn't involve the lives of more than 100 passengers who – along with engineer Mark James – were counting on the CSX conductor to make sure the tracks were pointing in the right direction for Amtrak to pass through.

Lesley Stahl: Is there anything that you should have done that you didn't do?

Mark James: No.

Lesley Stahl: Nothing.

Mark James: I can't see what my conductor's doing. And I have to trust him. We have to work together. And I did trust him. And he's human. He made a mistake.

What if we told you that mistakes like that, human errors, can be caught, and crashes prevented by a technology that was supposed to be in place by now. Congress mandated that most of the country's major railroads install the technology by 2015.

In a complex arrangement, Congress extended that deadline first to 2018 and now again to 2020. The technology is called positive train control – PTC.

It's a computerized system that uses technology like GPS and Wi-Fi to transmit information from sensors and signals installed along the tracks to and from the trains. It amounts to an automatic braking system.

Pat Desir shows correspondent Lesley Stahl how PTC works

Pat Desir, an engineer for the Southeastern Pennsylvania Transportation Authority, demonstrated how the system works.

Lesley Stahl: This is the speed limit and this is what you're going at the moment.

Pat Desir: Exactly. It enforces my speed.

Lesley Stahl: So it can stop the train, but it can also slow you down to keep you—

Pat Desir: Exactly.

Lesley Stahl: --at the right speed.

Pat Desir: See right now we're supposed to be doing 25 miles per hour. All right, I'm gonna go above it. And I'm gonna show you how PTC works. All right? I'll get to about 28 miles per hour. And I'm bringing it up. You feel (BEEPING) how fast we're going? And now-- (NOISE)

Lesley Stahl: Whoa.

Pat Desir: And we received a penalty brake application. Brought the train to a complete stop.

Lesley Stahl: Whoa.

This commuter railroad was one of the first to install the equipment. But others have been slow to follow. And that has led to deadly consequences. The PTC mandate was imposed after a crash in Chatsworth, California that killed 25 people. Since then, there have been 22 crashes, killing a total of 29 people and injuring more than 500.

If PTC had been installed, this derailment a year ago in Washington state - when Amtrak 501 was going twice the speed limit – wouldn't have happened.

And this crash in 2015 when an Amtrak train was going too fast in Philadelphia - wouldn't've happened either.

The major railroads – including CSX and Amtrak - each own miles of their own tracks and their trains ride on each other's tracks.

To make matters more complicated, they're installing different PTC systems and have to make them compatible with the other companies that ride on their tracks. They've also been stymied by software and equipment challenges and regulatory hurdles.

As of today only 10 percent of the mandated railroads have fully implemented PTC.

Lesley Stahl: It seems so obvious. It just seems so urgent that it's almost unfathomable that it doesn't get done.

Robert Sumwalt: That's why the NTSB is just flabbergasted that we still don't have it more than 10 years after Congress mandated Positive Train Control.

One issue has been the Federal Railroad Administration, FRA, the railroad's regulatory agency, criticized in government reports for not vigorously enforcing the PTC mandate. We tried to talk to the agency but they declined our interview request.

Its handling of PTC has been a source of frustration for Robert Sumwalt of the NTSB.

Lesley Stahl: The regulatory agency, The Federal Railroad Administration, are they just not doing their job?

Robert Sumwalt: Well, we have issued recommendations to the FRA and they've not acted upon those.

Lesley Stahl: Why are they so lenient with the railroads? Somebody told us that in his opinion they're captive to the railroad system, to the industry.

Robert Sumwalt: The regulator needs to step up to the plate and do their job and regulate.

Lesley Stahl: Who's responsible?

Robert Sumwalt: Well, ultimately, it's up to the railroads to put this system in place. It's a steep climb for them. It's going to cost, depending on who you talk to, anywhere between $10 and $14 billion for the system to be implemented.

Lesley Stahl: Okay. So?

Robert Sumwalt: You're right.

Lesley Stahl: I mean, it's safety. You're, they're, they have people's lives in their hands.

Robert Sumwalt: Yes, and we're confounded by that as well. And for every day that goes by we are at continued risk.

When there's a train crash involving Amtrak, it usually pays the damages. But because it is largely funded by the government, that means the taxpayers pay.

We have learned that Amtrak agreed decades ago, in secret indemnity contracts, to be responsible for damages even if the freight company is at fault and the accident occurs on the freight company's tracks.

The freight company in the South Carolina crash, CSX, declined our interview request, but sent us a letter saying it has already spent "$2.5 billion" on PTC and that the crash was "the result of human error, and violations of long-standing operating procedures." CSX fired both the conductor and engineer Mark James.

Lesley Stahl: Are you fighting this?

Mark James: Yes.

Lesley Stahl: Are you challenging--

Mark James: Yes.

Lesley Stahl: --the firing?

Mark James: Yes. There's nothing I could have done to prevent the accident. I did nothing to cause the accident and I got fired anyway.

James is unemployed. He's raising a teenage daughter and is facing large medical bills for PTSD.

Mark James: You can't sleep at night, you know. If you wake up, this is in your head.

Lesley Stahl: Still.

Mark James: Yeah, and nightmares, visions, like in – loud noises.

Lesley Stahl: Like a soldier.

Mark James: Yeah.

Lesley Stahl: In your opinion, is train travel safe?

Mark James: No.

Lesley Stahl: Would you put your daughter on an Amtrak train?

Mark James: No. I wouldn't get on one myself.

Amtrak, which declined our interview request, sent us a statement saying it has made substantial strides on implementing PTC.

Produced by Sarah Koch and Chrissy Jones