The December 2022 issue of IEEE Spectrum is here!

Close bar

Track circuits on four of the five Washington DC Metro lines have been found to exhibit "anomalies" which would prevent the Metro's central computer system being able to track the location of subway trains on the transit system, the Washington Post is reporting this morning. A total of seven circuits that have now been found to be not operating as designed.

Metro management had been insisting that the crash, apparently caused by a malfunctioning track circuit, was a "freak occurrence."

According to the Post, another troublesome circuit used to relay train location was found on the Red Line (the subway line on which the train collision occurred), as well as on the Blue, Orange and Green Lines.

Apparently, Metro doesn't know what is causing the problems, the Post says, although Metro management says that the problems aren't as severe as with the malfunctioning circuit associated with the crash. However, Metro has disabled some of the troublesome switches if they could not be repaired immediately.

As a result, the Post story says,

"When crews disable track circuits, they create "dark" stretches. That means trains have to proceed one at a time through the affected section of track at a maximum speed of 15 mph, which is creating delays. It also means that controllers in Metro's downtown operations center can't "see" the train as it moves through the affected area and that the safe operation of the train is entirely in the hands of the operator. Track circuits range in length from 400 to 500 feet up to about 1,000 feet, with shorter circuits closer to the stations."

At least one train control expert calls the disabling of train circuits "highly unusual."

Metro management, however, insists that the transit system is safe, and that the Post story "grossly exaggerates" the safety issues involved. However, as the Post story notes, Metro management has known about the track circuit problems for about two weeks, yet it had publicly claimed none had been found just a few days ago.

The Conversation (0)

Why Functional Programming Should Be the Future of Software Development

It’s hard to learn, but your code will produce fewer nasty surprises

11 min read
A plate of spaghetti made from code
Shira Inbar

You’d expectthe longest and most costly phase in the lifecycle of a software product to be the initial development of the system, when all those great features are first imagined and then created. In fact, the hardest part comes later, during the maintenance phase. That’s when programmers pay the price for the shortcuts they took during development.

So why did they take shortcuts? Maybe they didn’t realize that they were cutting any corners. Only when their code was deployed and exercised by a lot of users did its hidden flaws come to light. And maybe the developers were rushed. Time-to-market pressures would almost guarantee that their software will contain more bugs than it would otherwise.

Keep Reading ↓Show less