There have been many write-ups on the improper (and proper) use of the hazard lights on your vehicle.
The most notorious use of the hazard light function is during dense fog or heavy downpours. The rainy season is here and with it the tendency of some motorists to use their hazards while driving normally. While it may seem “safer”, using the hazards in such a way deprives you of the use of your turn signals or indicators, which is why you should never do it.
Many of us have written about this and called it out on social media, and this bad habit is now relatively rare, not common practice. Even during our many convoy drives where the drive master/lead driver instructs us to turn on our hazards, I will never do so for the same reason.
Your hazard lights are only to be used in instances like having to pull over to change a tire, have a car issue that forces you to park on the shoulder, if you're involved in an accident (hopefully not seriously), get pulled over by the police or traffic enforcers (gulp), and many more. Basically, so long as you are a hazard on the road because you need to stop, use it.
But there is another way to use your hazards that isn't exactly in the manual, and it's one that I've been practicing for the last 5 years or so. If done right, this can potentially save you the stress of a rear-ender or even a multi-vehicle pile-up.
Whenever I have to unexpectedly come to a complete stop on any fast road like an expressway, highway, or even an avenue like EDSA, I quickly turn on my hazard light and turn it off after about 2-3 seconds. Let me explain why.
The logic is simple: it is to warn the driver or rider behind that I have actually come to a full stop, and that the brake lights aren't just about slowing down. This is to tell the driver behind that he or she may need to come to a complete stop as well.
Some would say that's what the brake lights are for, and that is very much true. But at higher speeds, it can be confusing to distinguish whether the vehicle ahead is just slowing down or coming to a complete standstill. Using the hazard for that short burst should make it absolutely clear that you are stopping, and those behind have to stop too.
The key phrase here is unexpectedly stopped; on an expressway or highway, you don't normally expect to actually come to a full stop, for whatever reason. It's supposed to be free-flowing all the time. But there are instances where there is a sudden traffic jam due to things like debris or another collision that there is no warning for the vehicles coming up.
The tip probably won't prevent all rear-end collisions; each one is different, and sometimes it's unavoidable. But if there is a chance that it can help reduce the risk of a larger and more powerful collision, then what is there to lose by trying? This is especially useful if you have to come to a stop on the fast lane of the expressway. I've seen drivers have to take evasive action on the expressway (e.g. swerve to the NLEX median) because they misjudged that the vehicle ahead actually had to come to a full stop because of another vehicle.
Basically, it's a manual simulation of the emergency brake or blinker light function (typically called ESS or Emergency Stop Signal) found in some luxury cars and/or vehicles with advanced safety features. A lot of modern vehicles have a function where the hazards automatically turn on when you come to a sudden stop. Some models even have a function that pulses the brake lights three times when it detects full braking from higher speeds to tell the drivers behind that they have come to an emergency stop. And no, I'm not talking about those silly (and annoying) blinking LED bulbs you buy online.
I first observed this practice when riding shotgun with a friend in Malaysia; their vast network of highways makes it a high-speed “paradise” compared to our expressway network in the Philippines at the time. During our drive, he would quickly turn on the hazard if we encountered traffic unexpectedly, look in the mirror to see if the driver behind recognized the danger, and turn it off again after he's satisfied the driver behind responded by braking.
There was another observation from that time in Malaysia: when the driver did that, the driver behind would also do the same for the vehicle in the back. So much so that it can trigger a line of vehicles activating and deactivating hazards one after another behind you.
As far as I know, this practice isn't that common or performed around here, but I can say it can help prevent costly and painful rear-end collisions on roads with faster speeds. As our road network expands and average speeds increase, hopefully, this tip can help you out.