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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.