We are required to carry warning devices in our commercial motor vehicles. You must carry either fuses (flares) or triangles. Truthfully, I don't know anyone who carries flares any more. Triangles are just more convenient. You don't have to worry about getting them lit in a rainstorm. While you are required to have them you also hope that you never use them. Mine fit nicely in an orange box near next to my fire extinguisher. That way I can check them both at the same time during my inspections.
It is irritating to see a broken down truck by the side of the road with just the flashers on. It may be even more irritating to see a broken down truck on the interstate with 3 trianlges place about 5 feet behind the trailer. A breakdown is a hassle. Having someone run into the back of your vehicle is way worse, especially if YOU did not set up your triangles properly.
We have all seen diferent triangle set ups. I know that I have seen traingles set up in front of the truck on a divided highway. It isn't that hard people. The first traingle goes 10 feet behind the vehicle even with the left side of the vehicle. The second traingle goes 90 feet behind that - or about 30 paces. 40 if you are taking short strides in about the middle of the vehicle.. The third triangle goes 100 feet or about 33 good paces behind that one. It should be about even with the right side of the broken down vehicle.
Check out 392.25 in your regulation book. It gives all of the requirements. It also gives the proper placement in a given situation. When you breakdown set your triangles up immediately after you set your brakes even before you make the call for service. While the DOT technically gives you time - just set tham up right away. You would hate to have someone run into the back of your trailer while you were making a phone call. Traingles aren't complicated as long as you don't take them for granted.