The third rail is the extra rail running alongside the two standard rails that train wheels ride on. It carries electrical power to the train and is typically positioned to one side of the track, not between the two running rails. In most subway systems, it delivers around 750 volts of direct current, enough to cause fatal injuries on contact.
How to Spot the Third Rail
Every rail track has two “running rails,” the parallel steel rails that support and guide the train’s wheels. The third rail is a separate conductor rail positioned off to one side, mounted on insulated posts spaced roughly every 10 feet. It sits lower than the running rails and is not designed to bear the weight of a train. Its job is purely electrical: it feeds power to the train through a contact shoe that slides along its surface.
In most transit systems, the third rail has a protective coverboard over the top, a shield made of insulating material that prevents accidental contact from above. This cover is one of the easiest ways to identify it. The running rails are bare steel on top because the train wheels need direct contact. The third rail, by contrast, looks partially enclosed or hooded. There’s a gap underneath the cover where the train’s current-collecting shoe slides in to make contact.
The third rail also differs in construction. Many systems use a bimetallic design, steel and aluminum bonded together, which gives it a different color and texture compared to the solid steel running rails. It often appears lighter or more silvery.
Where It Sits Relative to the Platform
Transit designers deliberately place the third rail on the side of the track opposite the passenger platform. This means if you’re standing on a subway platform looking down at the tracks, the third rail is on the far side, away from you. This positioning reduces the chance of someone falling from the platform and landing on it.
In tunnel sections with maintenance walkways, the same logic applies: the third rail runs on the opposite side from the walkway. In rail yards where tracks run close together, the third rail is placed in the gap between adjacent tracks. The placement always prioritizes keeping the energized rail as far as possible from where people walk.
There are gaps in the third rail at certain points, particularly at switches and crossings, but these gaps are sized so the train’s front and rear contact shoes can bridge them without losing power.
How Much Electricity It Carries
Every third rail system in the world runs on direct current. The most common voltage is 750 volts DC, used in systems like London’s Underground and many U.S. subways. Toronto’s subway operates at 600 volts DC. Some systems push higher: San Francisco’s BART runs at 1,000 volts, Hamburg’s S-Bahn at 1,200 volts, and a few lines in Guangzhou and the Paris Métro reach 1,500 volts.
These voltages are far lower than overhead wire systems, which can operate at 25,000 volts or more. But the smaller clearance around a ground-level rail makes higher voltages impractical. The practical ceiling is around 1,200 to 1,500 volts for third rail systems. That’s still more than enough to be lethal.
Why Contact Is So Dangerous
Touching the third rail makes your body part of an electrical circuit. The current enters at the point of contact and exits where your body is grounded, typically through your feet. This creates entrance and exit wounds and causes deep tissue damage along the path between them. The damage is proportional to the intensity of the current flowing through you, not just the voltage.
Even without direct contact, an electric arc can form if you get close enough. These arcs can reach temperatures around 5,000°C, hot enough to cause severe thermal burns across a wide area of skin. In a 30-year study of high-voltage electrical injuries, people who contacted rail systems sustained burns covering nearly half their body surface on average.
The heart is the organ most at risk. When current flows vertically through the body (entering through the arms or head and exiting through the feet), cardiac failure occurs in about 38% of cases. A study published in the Journal of Clinical Medicine found that roughly 1 in 5 patients hospitalized for high-voltage electrical injuries experienced some form of heart failure, with abnormal heart rhythms being the most common complication. Damage to the heart muscle can also be subtle, showing up as elevated cardiac injury markers even when the person initially appears stable.
Survival Rates and Long-Term Outcomes
Contact with the third rail is survivable, but the injuries are severe. In a 30-year review of hospitalized patients with high-voltage rail injuries, the survival rate was 75% for recreational contact (such as trespassing on tracks) and about 89% for work-related incidents. The difference largely reflects how the contact happens: workers tend to touch the rail briefly with a hand or tool, while trespassers often sustain full-body exposure.
Survivors face long recoveries. Average intensive care stays in the study exceeded 38 days for non-occupational injuries, with patients undergoing an average of 5 surgeries. Over half required amputations. Kidney failure affected more than 40%, and about a third needed dialysis, because electrical injuries release proteins from damaged muscle tissue that can overwhelm the kidneys. Even those who recover from the acute phase often face years of rehabilitation and permanent disability.
Emergency Power Cutoffs
Most subway stations have emergency power cutoff buttons, typically located at both ends of the platform under a bright blue light. Pressing this red button de-energizes the third rail in that section. If someone falls onto the tracks, this is the most important immediate action a bystander can take.
Cutting the third rail power does not stop trains immediately. Operators may still coast into a station under momentum to avoid stranding passengers in a tunnel. So cutting power eliminates the electrocution risk but not the risk of being struck by a moving train. If you ever fall onto tracks yourself, moving away from the third rail (toward the platform side) puts distance between you and the energized rail while keeping you visible to the train operator.