The accident with the 20 foot truck isn't your fault since hindi ka naka-hazard lights. The problem of that is that the guy in that truck was driving too fast for the conditions and he assumed he could brake on time. Whenever we drive we take risks. How would you know the car behind you will not plow into you at any given moment? There is no way to really tell and prevent this. After all, of all people, ikaw ang may experience dito like you said.
Get it off your chest, it wasn't your fault that he hit you from behind. Others will agree that considering this, it is not wise to further add insult to injury by confusing others when you turn on your hazard lights when unnecessary just so you will not be rear ended again.
Honestly I see that you have a point that hazard lights may prevent rear end collisions in this case. But when you are moving and using the hazard lights, you are definitely not using the hazard lights properly. If a truck will hit you from behind, weather or not you have the hazards on, he will plow into you in extreme weather conditions if he doesn't brake on time. I'm sure you know that trucks need much more braking distance to stop. But consider too that their tires aren't really the best ones either, and that considering that we're talking about Philippine driving, the truck may be overloaded too and may require significantly more braking distance to avoid the collision.
mainit masyado ang balitaktakan dito. hazard lights pag emergency lang ako. malakas na ulan, hindi kasi kahit ako sumasakit ang mata samga naka hazard. hehehe...