Reports that a Red Line train went barreling through four stations without a driver on Thursday gave riders quite a stir this week. The mishap, believed to have been caused by operator error, birthed an MBTA controversy that was big even for an agency used to dealing with commuters’ scorn.

The facts so far suggest the operator, a T veteran of more than 25 years, rigged his controls – a swivel-mounted throttle – with some kind of cord. That choice, investigators believe, was the first in a series of errors that ended up sending what’s since been called the “ghost train” on its now-infamous journey.

T-minders noticed the error within a minute, killed power on the track and averted disaster. No one was hurt (the operator sustained minor injuries when he was clipped by his runaway train). The T pledged to never again let another train leave the station without a driver. But maybe that's the wrong idea. Maybe, an expert told Metro, trains shouldn’t have drivers at all.

“It’s not crazy,” said William Messner, a mechanical engineer at Tufts University specializing in automatic control systems. “From a technology standpoint, it’s certainly doable. It’s a question of expense, really, and of course public acceptance of autonomous trains.”

RELATED: Over 1,000 abandoned bikes found in Boston since 2011

Around the world, he said, there are transit agencies whose use “driverless” trains are that way on purpose, or will be soon.

Passengers on Vancouver’s SkyTrain can board fully automated rapid transit.

An elevated tram in Oakland hoists passengers on its Airport Connector in driverless cars pulled by cables

Officials in Mexico City are studying the use of automated gondolas as an alternative to building a subway. 

By the mid-2020’s, the London Underground expects to welcome fully driverless trains to the “tube.”

None of those cases are apples-to-apples comparisons, of course. And the MBTA, with its ancient infrastructure, is not exactly the perfect case study for robotic retrofitting, Messner admitted.

“This system was not designed to be autonomous,” he said.

Converting to an automated system could also come with an enormous price tag – this for a system currently facing a widening budget deficit and an expensive list of needed repairs.

"The MBTA has a $7.3 billion maintenance backlog. Our primary focus is to continue making the investments necessary to bring the existing vehicles and infrastructure into a state-of-good-repair," MBTA spokesman Joe Pesaturo said in an email.

RELATED: Red Line 'Ghost Train' Twitter account pokes fun at MBTA

Parts of the system are automated already – problems began for the “ghost train,” remember, when a glitch in the signal at Braintree station would not let the train pass. The train rolled away from the station only after its driver left the train to flip a “bypass” switch and override the system, officials have said.

Flipping that switch also overrode an automated system that would have stopped Thursday’s runaway train, had it come across another train ahead of it on the track, according to the T.

But converting to a full-on automated train system, Messner argued, could make for a safer, more efficient commute by removing or reducing the risk of human error altogether.

After all, he said, as we learned last week, the old-fashioned train-driver-working-a-throttle method leaves open the risk of controls being manipulated.

“It’s clear we’re more vulnerable than we like to believe,” Messner said.