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Why do interior lights on passenger trains go on and off?

Have you traveled by train and wonder why the train interior lights on passenger trains go on and off? Or when you arrive at a station, the train goes dark for a moment as you try to get off. This phenomenon happens not only on Amtrak trains but on commuter and light rail.

There is nothing wrong with the trains, and there is a very logical reason why this happens. Let’s find out what’s going on!

Amfleet 1
The inside of an Amtrak Amfleet 1 Coach Car found on many regional trains

Why do the interior lights go on and off on trains powered by diesel locomotives?

This article is not going into great technical detail because that is not the point. The purpose of this is to let the average traveler be aware of what is going on.

Efficiency

Amtrak's Hiawatha in Milwaukee, WI
Amtrak’s Hiawatha sitting at the Milwaukee Intermodal Station

If you are at a station, the main reason for the lights to go on and off is efficiency.

Passenger locomotives produce power using Head End Power (HEP) electricity for light, heating and AC systems, outlets, and more, and it is called hotel power. This system works well when traveling; it is not the most efficient way to supply power to cars when trains are sitting at stations for a long time.

Stations where trains sit for a while, are often equipped with cables to plug the passenger cars into power from a power plant.

Power at the station is called “house power.” By plugging the cars in at the station, the HEP does not have to run.

This move can be a significant saving for railroads by saving fuel and reduce wear.

When trains switch from “house” to HEP or the other way around, the lights will go off in the car.

There is a battery backup to run emergency lights and the PA system for the few moments the power swap takes. During this time there is not enough power for the toilets or other accessories.

Safety checks and more power

Sometimes trains have to go through safety checks, and often during these tests, the engineers may need to turn off the power to the cars temporarily.

Sometimes locomotive engineers will turn off the HEP if the train needs a little more power. The HEP can reduce the power going to the traction motors that power the train.

While you are traveling the lights go off

If it is later at night and the light goes off and doesn’t come back on, it could be because it’s nighttime! Amtrak will turn the lights off so you can sleep.

Passenger cars transfer power from one to the next via cables, sometimes these cables come undone during travel, which could cause the loss of electricity. Once the train stops, the crew can reconnect the line, and all will be well.

What about interior lights on passenger rail with electric trains and locomotives?

There are two ways electric trains get their power, either overhead wires or a third rail.

South Shore Line
A South Shore Line train going through the middle of the street in Michigan City, IN

An example of the third rail is Chicago’s CTA Subway/Elevated Lines. Each car makes contact with the third rail to get power for that car.

A train may lose power when going through a switch or crossing another track because the car lost contact with that power rail.

As soon as that car passes through that area, the power will come back on again.

Other electric trains use overhead wires; examples include the South Shore Line, Amtrak’s Northeast Corridor, and streetcars in San Fransisco.

Power loss on these trains can happen if the train loses contact with the overhead power. Other reasons include going into a dead block. A dead block is when an overhead line does not have electricity for whatever reason.

Wrap-up

I hope this answers your question on why do interior lights on passenger trains go on and off.

On one journey to Chicago aboard a Metra train, the hotel power went off because a cable came loose. Since it was not dangerous, they waited till we arrived at the station to fix the problem since we were close.

It is fun to hear first-time train travelers gasp when it happens. Now you know, and you can share this info with your travel companions.

Safe travels!
Kev

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Kev

Kev has traveled over 125,000 miles on over 660 trains all around the United States aboard Amtrak. When he is not on the move, Kev enjoys making music as an organist.