That may have actually changed:
"After more than 10 years of struggle, rental businesses finally declared victory on surge brakes in 2007. The U.S. Department of Transportation’s Federal Motor Carrier Safety Administration (FMCSA) in Washington, D.C., published final regulations that allowed surge brakes on all small and medium-sized trailers, even those used in interstate commerce. The new rules went into effect April 5, 2007.
FMCSA previously issued guidance and regulatory interpretations that made surge brakes illegal for use in interstate commerce. Many states, but not all, followed the lead of FMCSA and also outlawed the devices. The result was a patchwork of inconsistent regulations that allowed surge brake use by private individuals while banning the same devices in commercial applications. This created great confusion, problems and numerous fines for rental companies, as well as a difficult situation for trailer and boat manufacturers. All three groups came together to form the Surge Brake Coalition, an ad hoc group, to address and change the FMCSA rules"
"The US DOT has clarified the definition of what is a "brake" and surge brakes are not US DOT approved.
States that adopted the previous ruling as state law now have to decide how they are going to deal with this new ruling.
There is nothing inherently unsafe with surge brakes and the tests by DOT and others show they meet the required braking distances required.
"New rules took effect in April legalizing the use of automatic hydraulic inertia brake systems (surge brakes) on light- and medium-duty trailers within certain limits, even in commercial applications. Previously, the U.S. Department of Transportation's Federal Motor Carrier Safety Administration (FMCSA) had issued guidance and regulatory interpretations that made surge brakes illegal for use in interstate commerce.
"FMCSA, in previous rulings, had declared that surge brakes were not actually brakes," says John McClelland, vice president for government affairs, American Rental Association (ARA). "They didn't meet the definition of what a brake is."
At issue was a requirement in Section 393.48 of the Motor Carrier Safety Regulations that motor vehicle brakes be operative at all times. A surge brake, which is operative only under certain preset conditions, would not be in compliance with this requirement. Surge brakes, in general, are only operative when vehicles are moving in the forward direction.
Section 393.49 also required a single valve to operate all brakes. Guidance on this issue stated that since surge brakes cannot keep the trailer brakes in the applied position, the brakes on the combination of vehicles are not under control of a single valve.
These rulings soon spread to the state level. "A bunch of states adopted the federal rules for interstate transport simply by referring to them in their statutes," says McClelland.
This essentially banned surge brakes in these states. The result was a patchwork of regulations that often allowed use of surge brake-equipped trailers by private individuals, while banning them from commercial use. Due to inconsistencies between local regulations, there was a great deal of confusion as to when and where surge brakes were legal.
The new rules eliminate this confusion by spelling out the conditions under which surge brakes can be used. For trailers with Gross Vehicle Weight Ratings (GVWRs) of less than 12,000 lbs., the regulation approves surge brake use for vehicle-to-trailer GVWR ratios of 1:1.175. For trailers between 12,000 and 20,000 lbs., the regulation approves use for vehicle-to-trailer GVWR ratios of 1:1.25. "
Since the 2007 ruling, it's once again a maze of conflicting regulations, check here and hope it is current!
http://www.boatwheels.biz/brakelaws.pdf