OK! Disclaimer. I am not a US citizen and don't reside in the USA. I know my way around aviation regulations workwide, but am not really familiar with the rules for vehicles in the US. With all the different information around about different requirements in different states etc, I have been trying to understand this better myself (Opened a can of worms I guess) I have found these Federal Regulations. I just copied out the relevant items pertaining to trailers directly. Found at the following site https://www.ecfr.gov/ Title 49: Transportation PART 393—PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATIO 393.40 Required brake systems. (4) Electric brake systems. Motor vehicles equipped with electric brake systems must have a service brake system that meets the applicable requirements of §§393.42, 393.48, 393.49 and 393.52 of this subpart. §393.42 Brakes required on all wheels. (3) Any semitrailer or pole trailer (laden or unladen) with a gross weight of 1,361 kg (3,000 pounds) or less which is subject to this part is not required to be equipped with brakes if the axle weight of the towed vehicle does not exceed 40 percent of the sum of the axle weights of the towing vehicle. (4) Any full trailer or four-wheel pole trailer (laden or unladen) with a gross weight of 1,361 kg (3,000 pounds) or less which is subject to this part is not required to be equipped with brakes if the sum of the axle weights of the towed vehicle does not exceed 40 percent of the sum of the axle weights of the towing vehicle. 393.43 Breakaway and emergency braking. (d) Breakaway braking requirements for trailers. Every trailer required to be equipped with brakes shall have brakes which apply automatically and immediately upon breakaway from the towing vehicle. With the exception of trailers having three or more axles, all brakes with which the trailer is required to be equipped must be applied upon breakaway from the towing vehicle. The brakes must remain in the applied position for at least 15 minutes. Question is, are these the mandatory regs for all States.Any other regs from states can not be less than this. I don't know this and don't wish to start flame wars, so please give me your answer, but I would really appreciate a link to a document that would confirm any statement made. I have found a bunch of collated data on states and their requirements. But they all have different information and without links back to the original Regulating document, it is harder to verify.