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.
A long time in coming
The ruling was a long time in the making. The movement to legalize surge brakes for commercial applications was spearheaded by the Surge Brake Coalition, a group founded in 1998 and made up of trailer manufacturers, parts suppliers, commercial users of surge-braked trailers, trailer rental companies and trade associations representing segments of the trailer business. The ARA was one of the leaders in the Coalition.
The Coalition argued that surge brakes provide a safe, practical braking system for CMV combinations, especially when the trailer is likely to be towed by a variety of vehicles. For some applications, such as rental, it is impractical and cost prohibitive to install or adapt an electric brake control system on every towing vehicle.
Surge brakes, on the other hand, activate automatically when the towing vehicle brakes are applied; adapt to the weight of the trailer load; have fewer components; and require less maintenance than trailers with electric brakes. The Coalition estimated that over 25% of the rental trailer fleet is equipped with surge brakes.
To demonstrate that surge brake-equipped trailers meet the safety performance requirements, tests were developed, then conducted by a test laboratory in 1999 and 2000. The tests covered combinations of representative towing vehicles and trailers widely available in the rental market. Three aspects of particular interest were straight-line braking, braking on a curve and brake-holding on a hill.
Twenty two towing vehicle and trailer combinations were evaluated. The tests concluded that surge brakes limited to the GVWR ratios listed have sufficient braking capability to comply with the agency's stopping requirements. There were no braking stability problems, and they were able to safely hold their position when stopped facing uphill on steep grades.