What do train signals actually do?

”Signal trouble” is a phrase Long Island Rail Road commuters know well – it often is the cause of the delays and cancellations that frequently beleaguer riders .

But what do train signals actually do?

Signal systems control train traffic by providing critical information to locomotive engineers, and directly to trains on how to proceed. A functioning signal system is about as vital to the operation of a railroad as the tracks and train cars themselves, experts say.

“It tells them what speed they’re supposed to be going. It tells them if they should be stopping at the next signal. It tells them the traffic conditions ahead of them so they can control their train accordingly,” Natale said. “You could not run a railroad without them.”

Signal problems

Since Jan. 1, the LIRR has cited “signal trouble” as the reason for service problems on at least 60 different days.

A major signal problem can be especially disastrous, as seen on May 10, 2017, when a signal problem involving one train led the LIRR to cancel nearly 90 trains during the PM rush, resulting in dangerous crowding in Penn Station.

And this is what a signal system looks like:

The pattern and sequence of red, yellow and green lights displayed on a signal direct a train on where to go, at what speed to travel, and what conditions are ahead.

An outdated system

But much of the LIRR’s signal system, including at Penn Station, relies on decades-old technology, including electrical wiring installed in the 1930s.

Penn’s 80-year-old railroad signal system is a complex electrical network of wires and colored light displays that performs a critical function — providing vital information to engineers, and directly to trains, on how to proceed. At complex rail junctions, or “interlockings,” signals are controlled by dispatchers monitoring train movements from control centers or towers.

Newer, computer microprocessor-based signaling technology could allow the LIRR to run more trains and more closely monitor them.

While Penn’s owner Amtrak is taking this summer to complete track work, the project will not involve its signal system, which experts say is in dire need of renewal. Amtrak has said it is trying to develop plans and a budget to do so.

To not have a plan going forward for the signal issue, I think, is a looming catastrophe.
– Sen. Todd Kaminsky (D-Long Beach)