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Why are hazard lights how they are?
June 19, 2014 3:36 AM   Subscribe

Picture the scene: you are passing a line of cars, and one of the cars has its indicator light flashing. You expect it to pull out. As you pass you notice that both indicator lights are flashing: the car's hazards are on. Why aren't hazard lights easier to distinguish from indicators?
posted by devnull to Travel & Transportation (13 answers total)
 
Do you want to get me started about how a brand-new $40,000 Chevy Volt can't afford two bucks of yellow plastic for the turn signals ?

I'll bet the real answer comes from the heritage of flasher relays.

But the hazard indicators still had the correct effect on the overtaking car, right ? You treated the hazard-causing car as a hazard.
posted by Kakkerlak at 3:40 AM on June 19 [2 favorites]


Hazards are used infrequently, and were probably a clever reuse of both signal indicators at the same time, never deserving of their own distinct lights.

You took notice their indicators were flashing, that got you to notice the car and be more careful. Would you have noticed it any differently if their hazards were on?

Plus, using lights properly is out of fashion. Don't use them and surprise the other drivers! or fake them out and leave your turn signals on for miles! Makes driving more exciting for all around.
posted by TheAdamist at 4:25 AM on June 19 [4 favorites]


Yeah, the heritage answer makes sense - or: it's a result of path dependency in the development of cars.

1) At some point, they introduced indicator lights.
2) The presence of indicator lights gave them the idea to create simultaneously flashing hazard lights. They were inspired by, and used, what was there, with a few minor adjustments.
3) That's how it stayed.

Looking around with a critical eye reveals rather a lot technological solutions with this quirk - solutions that make more sense when we follow the path of their development, than when we look at how well they actually work. (I once spent a whole evening discussing grand piano actions with a Danish engineer, who claimed that one could make a radically more simple action by simply forgetting about the solutions of the 18th and 19th century and beginning from scratch.)
posted by Namlit at 4:26 AM on June 19 [3 favorites]


> Do you want to get me started about how a brand-new $40,000 Chevy Volt can't afford two bucks of yellow plastic for the turn signals ?

How about why manufacturers seem to keep forgetting how to run brake and turn signals to separate lamps?
posted by FlyingMonkey at 5:13 AM on June 19


you are passing a line of cars, and one of the cars has its indicator light flashing. You expect it to pull out. As you pass you notice that both indicator lights are flashing: the car's hazards are on.

The issue is more that the hazards are being incorrectly used in this context. The lights are to tell other drivers that a car is not necessarily what it seems - ie a stationary car when it is in a position where it should be moving, or a car going slower than normally expected. A single car in a line of others is not an unexpected hazard (unless it is coming out, in which case indicators are appropriate) and so the use of the hazards in that situation is more hindrance to understanding than help. That is not a situation where hazard lights should be on, so them not being distinguishable is not so much of an issue, but the incorrect usage of them is.

So really the distinction between hazards is irrelevant - after all, if you'd known they were hazard lights instantly rather than indicators, you'd have just driven past and probably thought "why did he have his hazard lights on when he's just parked like everyone else?". The process would have been the same, just minus the shift in understanding of what lights are on.
posted by Brockles at 5:14 AM on June 19


Do you want to get me started about how a brand-new $40,000 Chevy Volt can't afford two bucks of yellow plastic for the turn signals ?

The NHTSA does not require rear turn indicators to be yellow.

It's not a question of "can afford", but one of why would a corporation spend extra money on yellow lenses, bulbs, and wiring harnesses across millions of vehicles produced every year. That adds up to some real money.
posted by Fleebnork at 5:27 AM on June 19


hazards are being incorrectly used in this context

Incorrectly, yes, but it is becoming more common. I'd like to see a unique blinking pattern for hazards that differentiates them from turn indicators, or as I call them, blinkers.

I have similar issue with Metro Transit buses here in the Twin Cities. When they are stopped for passengers, there are two blinking lights on the rear of the bus. If the right light is blocked by another vehicle, I don't know if they have their left blinker on or not. Once they do put their left blinker on, there is a light on the side of the bus that also blinks, but when there is just a blinking rear light, I often assume they may be pulling out. Yielding to a bus leaving a stop with its blinker on is the law here in Minnesota, so there is always a second where I assume it is a blinker until I can verify the side light is not flashing.
posted by soelo at 9:35 AM on June 19


Actually I think the combination of turn signals and hazard lights is a stroke of design genius: A turn signal is an indication for you to pay attention to where this car is about to go. Both directions on just escalate this to a the next level of seriousness - it says I'm going to be doing something unexpected. It makes a lot of sense to have the two signals share vocabulary.
posted by Dr Dracator at 11:32 AM on June 19


Hazards convey similar but different information to turn signals. My question is why this information is discarded in some situations, and why we haven't got something better - a different pulsing sequence, or some other way of showing the information.
posted by devnull at 12:15 PM on June 19


As mentioned above, the original pulser was a very simple RC circuit relay arrangement - if you come across an older car with one of the flash bulbs burned out, it flashes twice as fast! A different pulse sequence would be too complicated to implement back then, and you can't change it now due to inertia, both cultural but also probably legal: I'm speculating here, but an alternative pulsing sequence could very well be out of spec as far as licensing is concerned.
posted by Dr Dracator at 12:56 PM on June 19


Actually, the original pulser was a bimetallic strip...
posted by Brockles at 1:56 PM on June 19


Hope this isn't a derailment, but an expansion on the design of hazard lights and their heritage to directional signal lights...

For newer cars that have turn signal lights on their side-view mirrors, or long trucks with several turn indicators along their length, do they all flash when hazard lights are on? Is it consistent across makes and models? I have not had a chance to notice this myself (maybe an excuse to go tire-kicking...)
posted by WasabiFlux at 8:37 PM on June 19


Besides the cost savings integrating hazard lights with the turn signals means they are more likely to work when you need them. After all most people rarely if ever use their hazard lights so a burned out bulb, blown fuse, or loose connection would never be noticed.
posted by Mitheral at 8:55 PM on June 22


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