Since I was looking at railroad crossing lighting at ebay, and I was looking at a item, which is a railroad crossing gate light, and its input voltage is 8 to18v AC/DC. Are railroad crossing lights low voltage? I know traffic lights take mains voltage (120v).

I know that our railroad crossing lights, are halogen, based on their wig-wag flashing appearance (Their flashing looks like dimming and brightening rather than switching on and off). I don't know if they are 230V or low voltage, but I know that the bells makes 3 rings per sec, rather than 50 rings per sec like most electro-mechanical bells.

Here all the railway signals (not only those for crossings, but including those rail traffic safety control ones) are using regular mains voltage for all the feed lines and then there are transformers in the base of each pole (one transformer per bulb), feeding then ELV bulbs.
The ELV bulbs are used mainly for their higher vibration resistance and smaller radiating surface (to allowprecise selective signalling on e.g. multitrack lines - the drivers see or at least are able to distinguish the lights valid for their track), plus thededicated transformers allow to finetune the operating voltage for each lamp individually and even compensate for wiring drop.
But dunno how exactly the modern LED signals are wired there (the system needs reliable diagnostic, which is rather simple with incandescents, but becomes quite complex with things like LED or so).

And I strongly doubt this concept was invented here, I would guess the same is (or at least was) used elsewhere as well.

I believe they still operate on low voltage to this day. At least the large national networks in the US. I am unsure about light rail or regional/monopolized systems.

Railroad signals (at least in North America) are low voltage.  There could be a serious accident if the signals fail to light due to a power outage, they are actually run off of batteries.  The batteries power the lights, gates, bells, and track circuits, and the power supply connection is there to maintain the battery.

The dimming appearance of filament bulbs is due to how the lights are wired.  The right and left signals are actually connected in series with each other, with the wig wag switch being in the middle, and alternate the middle (between bulbs) between positive and negative.  During the moment that the switch is in motion, the bulbs light dimly together, as they are now energized in series with each other.  Again this is done for fault tolerance.  If the relay contact should fail on one side or the other, the lights won't wig wag, but one light will be stick shining bright.  If it fails in the middle, the both lights will light up together dimmer than normal, but there will still be red lights.

The LED signals are designed to use the same control equipment.

"Serious accident could happen in case of signal malfunction due to power failure"
Are you serious the system (here I mean including the laws and rules for drivers etc) is designed so stupid than such primitive failure as just aloss of power could lead to an accident?

Here the loss of power means just the trains get stopped on a first signal (a signal post with nothing alight is defined in the law as equal to a red light (or a yellow "prepare to stop" on a post that is not equipped with the red; on each post there is a sign telling which type it is), so train must not pass (if it is as too close it means emergency brakes and the case is then commission examined the same way as running red light, just in this case the driver is obviously legally OK, but all must be properly logged as apotentially dangerous event).
On the road crossingd the all lights off means for the road users the same as if the crossing is not equipped by any signal at all -so before entering and passing the driver must make sure there is nothing approaching on the tracks,...
So loss of power is supposed to jjst stop the traffic, but it shoukd not make any dangerous situation by itself.

I would be surprized if the same concept would not be used elsewhere as well. So then the "not working signals" are just an excuse making from  the offenders and not the real cause...

I think track signals still use low voltage and redundant power supplies, and not all rail lines are signaled.

I think track signals still use low voltage and redundant power supplies, and not all rail lines are signaled.

I don't think the low voltage is anywhere else but just locally in the signal posts. The plain reason why I think so is it would be impossible to deal with the wiring resistances across the lines, we are talking about few km long wiring for just one signalling section.

Yes, there is of course a backup for the public power grid supply, here in the form of generators (which are started roughly minute after an unexpected power failure, so the signals are not working for that minute) and at least two feed points from the public network (so unexpected failure of both at the same time is very unlikely, the genset is started already when one feed point is failing) in busy parts of the system, so there is no traffic blockage due to not working signals.

In Seattle, we deal with RR and LRT signals.

LRT (Light Rail Transit) are almost always 120vac, and we either drive them with traffic signal load switches or relays, depending on their control source.
Originally, our indications were special ordered through Hanning and Kahl, because I think in Europe everything is 48v or lower and we spec'd 120vac. Now, Dialite supplies our LRT indications

RR is low voltage. I believe it is 12VDC due to the battery storage systems they use. The signals are almost always operated off of 12vdc, and the 120VAC only keeps the batteries charged. This allows a seamless transfer to storage power in a power outage. We also provide them with 12v monitoring for our interconnected traffic signals, and, rarely where they use traffic signal vehicle detectors, those are EDI Oracles that run on 12VDC.

Everything related to RR is "fail-safe" so if anything totally loses power, the system will revert to safest state condition when possible.

I didn't know that RR signals have batteries during a power outage. Are they still connected to the battery while power is on to the power supply to change the batteries? Just being curious.

I didn't know that RR signals have batteries during a power outage. Are they still connected to the battery while power is on to the power supply to change the batteries? Just being curious.

All RR systems, as far as I know, run directly off of the battery banks. The charging system is in parallel with the batteries. So, there is little chance of service/power interruption.

BTW, I am not a RR signal tech, I am a traffic signal tech, but I do go into the RR wayside cabinets and I poke around a bit. These are my observations.

Everything related to RR is "fail-safe" so if anything totally loses power, the system will revert to safest state condition when possible.

And don' forget the "fail safe" is in most cases mainly in the rules, how the signals are to be interpreted in the different situations (so here the nonworking signals on the track have the same meaning as "stop", etc...), so the system safety design focuses on the signals to not display "go" when they should not, the missing power is the not a thread (but it practically halts all traffic, hence the backup supply is still installed).