What Do Railroad Signal Lights Mean?

As trains have developed over the centuries, so have train signals, also known as the traffic lights of the railway. An understanding of railroad signs is not only crucial for engineers, but it can also benefit passengers. Whether you are riding the Amtrak to work, hopping aboard an international train or waiting to cross one of the 140,000 miles of U.S. train tracks in your car, understanding railroad signals can benefit your safety. It also can help you understand why your train is slowing down or stopping (Hint: it usually has to do with safety). Here’s what you need to know:

Tip

When in doubt, remember that the colors for railroad lights are universally recognized. Similar to traffic lights, red means “stop,” yellow means “slow” or “caution,” and green means “go.”

The first train hit the tracks in 1804. A steam locomotive transporting iron material and 70 passengers in South Wales, it chugged along for 10 miles, bringing with it a new era of commercial transportation and travel. Shortly after, the Baltimore & Ohio Railroad opened as the first U.S. railway. For safety, trains were operated “on-sight,” meaning the driver watched for other trains and obstructions on the track. This system was prone to accidents, though and, in 1832, one of the first official railway signs, a ball-type signal, was implemented.

Like traffic lights for automobiles, train signals were created to prevent accidents and inform drivers of when the track ahead is clear. While railway lights are more complicated and vary in different parts of the world, colors are universally understood to mean the same thing: red for stop, yellow for caution and green for go. Passengers can also take comfort in knowing track circuits, designed by William Robinson in 1872, help keep trains from colliding. Each section of the track, called a “block,” is guarded by railroad signals, so the engineers know when it is safe to proceed.

A semaphore works as a moving arm mounted to a mast. A Victorian-era train signal from the mid-19th century, different positions at different angles inform the engineer of when to stop, proceed and travel with caution. Some also work in unison with lights. While most have been or are being replaced by digital technology, semaphores are still scattered across the globe today, including in the United States, United Kingdom and India. It can be helpful to recognize one when you see it.