Lets work on some clarifications here with the issue of surge brakes.
Back in the 1950's or so, a standard for *COMMERCIAL* truck brakes was set. It was clumsily worded, and was interpreted to be a complete absolute prohibition on braking systems that were not actuated by the main truck. This requirement for *COMMERCIAL* trucks is why vacuum brakes are #1, and electric brakes are #2. Both are controlled from the truck, while surge brakes are self contained on the trailer.
In relatively recent years, *ONE* individual took it upon himself to declare that surge brakes were illegal across the board, including for private non-commercial use. Interesting, as the regulations did not support this individuals claim. The regulations he was basing his interpretation on were for commercial use only. None the less, a good bit of uproar ensued. Companies like U-Haul were particularly concerned as they commercially rented surge brake equipped trailers to individuals. The commercial ban on surge brakes had always been a sticky-wicket for them, one they danced on by claiming the trailers were not in commercial use.
It was put to rest officially and finally, with 49CFR571. This federal regulation specifies the requirements of the fully legal surge brake systems. One of the most notable changes was in the definitions of commercial use, being revised to freight and motor carriers engaged in the transport there of.
So again, as previously noted, surge brakes are indeed legal on a federal level. You cannot use them on your semi if you are hauling freight commercially.