When traveling on a train in a storm, one may wonder if it is safe to be inside a passenger car with steel wheels, riding on steel rails. Therefore, this is understandably an area of great concern.
Are trains safe in lightning? Yes. If lightning was to strike a train, the electric current would travel through the train’s structure because of its steel construction which is conductive. Additionally, because the train has steel wheels and travels over steel rails, it is grounded.
Traveling on a train during a thunderstorm is completely safe. The train is extremely conductive and will absorb the strike. In fact, unless your house has a lightning rod, you would be safer on a train during a storm.
A bolt of lightning can strike within a five mile radius, reach astronomical temperatures, and contain millions of volts. Although the lightning will not cause harm to people aboard the train, a direct lightning strike could be harmful to the electronics and other elements of the train, causing delays and failures. Trackside relay boxes and wayside equipment would be susceptible to a lightning strike as well.
On a non-electrified railway, signals would be the most likely target for a strike, although the circuits are well insulated. On an electrified railway, a lightning strike could cause a plethora of issues if the overhead wires are struck. This could cause the entire rail line to lose electricity, therefore, bringing all trains to a halt.
A common myth is that because rail lines are not the highest metal object, for example, a lightning rod, that they are not susceptible to strikes. However, due to its unpredictability, lightning can strike track as well, however, it will usually do minimal damage to the train, however, it may set off grade crossings and other circuits.
Railcar Construction and the Farraday Cage
Many modern railcars are constructed utilizing a “Farraday Cage”, which blocks the effects of a lightning strike from the interior. This metal enclosure prevents the various currents caused by a strike, and directs the electrical current to the outer portion of the train, thus, although the voltage rises, the current does not pass through its interior. The train’s electrical system may experience damage or trip a relay switch.
The Farraday Cage, invented by scientist Michael Farraday, is a theory stating that when conductive material is continuously distributed throughout, it acts as a barrier that prevents the current from entering the interior. This theory holds true with trains, as the steel structure acts as a cage, where the current surrounds the outside steel structure of the train. So, when a train is struck, the electric current travels around the steel structure, which then travels towards the wheels and out onto the track.
The components of the train that would have the potential for damage are electrical circuits and fuses, causing them to melt as a result of the electrical surge, especially those that are unshielded.
Preventing Lightning Damage
Because of the vital role of wayside devices trackside, which supply the railroad with time sensitive information, an outage caused by a lightning strike would prove troublesome. These trackside mechanisms utilize components that have difficulty withstanding the effects of a lightning strike, and is costly to repair or replace completely. Therefore, railroad companies have enacted a variety of safety measures to prevent damage to this vital equipment.
Prior to the modern microprocessor controls that dominate the rail industry worldwide, older electronics could better withstand the strikes, as modern equipment is increasingly prone to a surge. Perhaps the most crucial piece of equipment that must be kept operable is positive train control, which is critical to the safety and well being of both passengers and crew.
Most railroads in North America must protect their wayside and other equipment from lightning, especially those in the mid-western and south-eastern United States. Lightning strikes could delay trains and cause large financial losses of revenue. Oftentimes, signals and similar equipment are most susceptible to strikes. The lightning will strike either the wires utilized by the signals on the track or buried underground, however, with railroads soon realizing lightning strikes as plaguing issues, they have searched for remedies to combat high profile disruptions throughout their networks. More concerning, communications could be hindered due to a strike, making contacting train crews and other personnel difficult or even impossible.
Unfortunately, it is not feasible to mitigate the risk completely, however, railroads attempt to reduce lightning induced damage as much as possible. According to Progressive Railroading, to prevent lightning strikes from damaging vital equipment, various companies have developed products that divert lightning strikes away from these mechanisms. These products include lightning attachment points on the roofs of railroad owned properties, and grounding devices that sends the energy produced by the lightning into the ground. These devices are primarily installed around yards where AEI readers, switch machines, and other wayside devices are present, as they are vital to the yard’s operation.
Protection against lightning strikes is more crucial due to radio frequencies needed for positive train control (PTC). Before PTC and other safety mechanisms, railroad companies would utilize gas tube radio frequency (RF) protection, however, this protection was short lived, and needed to be reapplied often in order to prevent the voltage from a strike from damaging the equipment. If a radio began to malfunction or fail completely, it would not hinder the safety of everyone on board.
However, the new 220 MHz radios utilized by PTC is a crucial safety feature and must be functioning at all times, thus, railroads are investing more research and funds towards protecting these devices. According to Progressive Railroading, the new forms of protection are a sophisticated hybrid of metal oxide varistors (MOV), and silicon avalanche diode (SAD). This hybrid encompasses high strength and gives the maximum protection against surges, and does not require any special maintenance.
Some companies are also including lightning surge resistance into their products. The most prominent being a built-in transient protection board, which redirects currents that will push itself through the other forms of protection.