Getting Ready For Underride >By Bruce Sauer

Aug. 1, 1997
It's easy to build a rear underride guard that is strong enough to meet NHTSA's underride regulations. The focus now is on designing a guard that cushions

It's easy to build a rear underride guard that is strong enough to meet NHTSA's underride regulations. The focus now is on designing a guard that cushions the impact. Here's what a number of trailer manufacturers are doing.

JANUARY 26, 1998. It is a date that trailer manufacturers are eyeing as they prepare to equip their trailers with underride guards that meet the requirements of two new federal motor vehicle safety standards.

FMVSS 223 and FMVSS 224 are the two regulations that will set new standards for rear impact guards for trailers rated over 10,000 pounds GVW. FMVSS 223 spells out the physical and performance requirements of the guards, while FMVSS 224 specifies how and on what types of trailers the guard should be mounted.

As the effective date of the rulemaking approaches, individual trailer manufacturers are at various stages of readiness. Some trailer manufacturers have been working on underride guards for years and are virtually ready. Others simply have some refinements to make on existing designs to be ready for the regulations. Some manufacturers are discovering that complying with the regulations may not be an easy task and are concerned that they may not be ready with a guard that they can legitimately certify.

"Trailer manufacturers will have absolutely no problem designing a guard-as long as they don't fly by the seat of their pants," one trailer manufacturer declared. "But when we approach underride conscientiously, we discover that there are a lot of things about this regulation that are difficult to overcome. We can't just slap a certification label on a trailer and say that the guard complies."

The main area of concern is the requirement that the guard be able to absorb "by plastic deformation" a specified amount of energy. Unlike other provisions of the coming regulations that NHTSA has considered proposing for years, the energy absorption requirement is a new wrinkle that was included in the final rule published in the January 24, 1996 Federal Register.

Concerns about the standard involve several areas, including:

*Energy absorption. Designing a guard that meets the dimensional specifications is straightforward for most types of trailers, but the energy-absorption requirements will involve significant engineering.

*Custom trailers. If a one-of-a-kind trailer requires modifications to a standard guard, how much additional time will be required to test and certify a guard that the manufacturer might never build again?

*Test facilities. FMVSS 223 details the process that guard manufacturers must undergo to certify that the guard complies with the strength and energy-absorption standards. The regulation calls for a rigid test stand and a device that applies force at a rate of no slower than 0.04 inches per second and no faster than 0.06 inches per second.

*Is this trailer exempt? As manufacturers have been thinking through what is involved in complying with the requirements, some trailers that on the surface appeared exempt from FMVSS 223 and FMVSS 224 may require rear impact guards. An example is a dump trailer with a rear spreader pan. One manufacturer had thought dump trailers would not require an impact guard. However, he points out that the addition of a spreader pan could place the "rearmost extremity" of the trailer 18 or 20 inches behind the rear wheels. Trailers are exempt from the regulation under the "wheels back" provision of FMVSS 224 if the rear tires are mounted within 12 inches of the rearmost extremity.

*Operational limitations. Manufacturers as well as trailer customers are concerned that the 22-inch ground height limit will restrict maneuverability-particularly that of 53-ft trailers. The current "DOT bumper" provides 30 inches of ground clearance. "Can you imagine the bumper damage that will occur when a 53-ft van trailer enters or leaves an inclined driveway with the slider moved forward?" one trailer manufacturer said. "And as of right now, it looks like any damage to the bumper will be considered an out-of-service item during a roadside inspection."

Stages of Readiness Trailer manufacturers were in various stages of readiness six months before the standard took effect. But even the leading manufacturers have work to do to get ready for January 26.

"Our design has been in compliance with the minimum strength requirements of the coming mandate for the past four years," says Dan McCormack, testing manager at Great Dane Trailers. "As soon as NHTSA introduced these standards, they were adopted as a TTMA practice and immediately implemented as a Great Dane standard-some 46 months prior to the effective date of the regulation."

Great Dane's tests indicate that its rear impact designs are exceeding the minimum strength requirements of the standard by more than 25%, depending on the type of trailer and whether the test point is at the vertical member or centered on the guard.

"Our largest volume trailers are ready," says Rod Ehrlich, vice-president of engineering at Wabash National. "But we manufacture a wide range of vans and platforms-equipped with a wide range of guard designs. All of them meet the strength requirements, but we have not tested all of our designs for energy absorption. Each of these designs have been or will be tested so that we know that they perform as required."

Such a policy means Wabash will be engineering and testing rear impact guards on an ongoing basis. As customers request trailers with specifications that dictate changes to the guard or its attachment points, additional testing will be required.

Some applications will meet NHTSA's requirements more readily than other types of trailers.

"We have found that it is easier to certify vans than flatbeds," Ehrlich says. "And the lower the deck height, the more difficult it is to design a guard that meets the requirements for energy absorption. Longer vertical members make it easier to manage energy absorption."

Using Existing Designs Utility Trailer is in the process now of testing the impact guards mounted on trailers. The company manufactures dry-freight and refrigerated vans, along with platforms.

"We have reason to believe that our current guards will meet the requirements," Gene Lewis, manager of product development, says. "We have been following the progress of this proposal all along. Our existing guards meet the strength requirements. The only ambiguity has been the energy-absorption requirements that NHTSA introduced into the rulemaking. Between finite-element analysis and physical testing, we believe that our current designs will meet or come close to meeting even the energy-absorption requirements. If they don't, we should be able to comply with a few adjustments to our designs."

Lewis said Utility has built the device required to test its rear impact guards and currently is conducting tests with the guard mounted on the trailer.

Smaller Manufacturers Struggle Some of the industry's smaller manufacturers are having difficulty meeting the energy absorption requirements of the new rulemaking.

"There is no way we will be able to comply," one small manufacturer declared. "We don't make a standard product, and we don't have the resources to do the testing."

"We don't know what we are going to do," another said. "Most of our trailers are 'wheels back' vehicles that are exempt from the regulation. But size and weight laws sometimes make it impossible for us to build trailers that customers want without moving the wheels forward. What are we supposed to do in those cases? We don't have the engineering staff to justify designing and testing underride guards for the few trailers we make that will require them."

Another small manufacturer, however, was scheduled to be ready for the regulations in August.

"We have completed our engineering and are doing the testing now," says Bud Reitnouer, president of Reitnouer Inc. "We may have to tweak our design slightly, but the basic design is in place."

The company specializes in manufacturing platform trailers. Reitnouer says designing a guard to meet the requirements of the regulation required a minimum of 100 manhours, much of which was spent conducting finite element analysis.

Establishing a Need NHTSA estimates that the dual safety standards will prevent between four and 15 passenger compartment intrusion fatalities annually when all applicable trailers are equipped with compliant rear impact guards.

Opinions about the frequency of rear underride accidents vary significantly. According to data released by Citizens for Reliable and Safe Highways (CRASH), an average of 500 people are killed per year as a result of truck rear impacts and rear underride. Between 1980 and 1990, CRASH says that these accidents resulted in more than 5,000 deaths and 180,000 injuries.

TTMA found that some of the data being cited lumped trailers in with a wide range of GVW ratings. It also included head-on collisions between the tractor and another vehicle-accidents in which the design of the trailer was not directly responsible.

To resolve some of the ambiguity, TTMA commissioned Failure Analysis Associates to study every fatal accident in the Fatal Accident Reporting System database. In a report issued in 1995, before NHTSA issued its final rule, the consulting company reported these conclusions:

*Between 1975 and 1993, 79,288 heavy trucks were involved in fatal accidents.

*Of those, 62,227 were involved in collisions with other motor vehicles.

*Of the 62,227 collisions, 7,859 were struck from the rear by other motor vehicles, resulting in 8,046 fatalities.

*Of these 7,859 heavy trucks, 6,351 had trailers. These resulted in 6,557 occupant fatalities.

*Of these 6,351 rear-end collisions, 446 were cases where the vehicle underrode the trailer, resulting in 505 occupant fatalities.

*Average annual fatality rate between 1978 and 1993 for rear underride accidents was 32 per year. Underride data were not available prior to 1978.

*Approximately 85% of drivers who were killed in the underriding vehicles were not wearing seatbelts.

*Drivers of the underriding vehicles were cited for reckless driving or speeding in two-thirds of the fatal accidents.

*Alcohol was involved in approximately 50% of the accidents in which the driver was killed.

Early Returns Predictions that new rear impact guards will carry both cost and weight penalties are not totally true.

"Some of our guards will weigh the same as our existing designs," Ehrlich says. "All of them meet the minimum strength requirements. Some will require changes in configuration in order to control deflection, but these changes generally will not affect the weight appreciably."

Reitnouer trailers will neither cost more nor weigh more because of the rear impact guard.

"Our design is different from that of most manufacturers," Reitnouer says. "We connect it to the trailer at four points instead of just two, but the overall weight-and cost-is about the same."

Ehrlich points out the cost trade-offs involved in rigid guards.

"Cost of the guards depends on the approach the designer takes," he says. "Guards that bend and stay there will be less costly initially, but the maintenance costs will be high. A guard that absorbs energy through restorable devices will cost more to buy, but maintenance costs may not be as great."

Clearly cost and weight differences for compliant rear impact guards are negligible for those manufacturers that will be using existing designs. For other manufacturers, costs, weight, and other variables will be changing in coming months.

"The energy absorbing requirement, the controlled deflection, the test standards set in the regulations; and the certification all combine to present smaller OEMs with a huge challenge," one trailer manufacturer says. "Other people must be as worried and confused as I am, but I don't want to be the first to admit it."

Should trailer manufacturers test rear impact guards to real-world conditions or to the letter of the law?

In preparation for more stringent requirements for rear impact guards, some manufacturers are testing their designs on the rigid fixture specified by NHTSA rulemaking. Some, however, are seeing how the guards perform when mounted on a trailer. One reason: to more accurately reflect the way the guards will perform in real-world situations-motorists do not crash their cars into impact guards mounted on rigid fixtures.

"We are testing our designs on trailers and on a stand," says Rod Ehrlich, vice-president of engineering at Wabash National. "Trailer frames are not absolutely rigid, which should be a factor when evaluating the guard's energy-absorbing characteristics."

Several other trailer manufacturers are testing trailer-mounted guards.

"We test them on a test stand because that's what the law says," says Jimmy Yglesias, director of product systems and components at Great Dane Trailers. "But we test them on trailers so that we know how they will perform in the real world. It is important what part the trailer structure plays in preventing trailer underride and what its contribution is when the guard and trailer structure are considered one system."

"Guards perform differently when put on a trailer," says Dan McCormack, testing manager at Great Dane Trailers. "Deformation of the trailer may absorb more energy than the guard itself in some configurations. The failure modes are quite similar, regardless of whether the guards are mounted on a test stand or on a trailer. When subjected to forces that exceed those required by NHTSA, the tendency is for the rear vertical member to tear at the buckplate of the trailer."

To test underride protection fully in real-world conditions, however, is a staggering task. Among the variables affecting the ability of the guard to protect the people inside the automobile: speed, weight, and height of the vehicle. What happens if the guard is struck by a Ford Festiva? What if the vehicle is an F-350?

"One important variable in real crashes is the angle of impact," McCormack says. "We calculate strength requirements and energy absorption based on impacts coming directly from the rear of the guard. But when the car hits the guard at an angle, all the stresses change. The number of scenarios that we could design for becomes enormous."

The regulators who wrote NHTSA's rear underride rulemaking did so acknowledging the possibility that one company could manufacture the guard and another company install it.

With the effective date of FMVSS 223 and 224 just months away, Elvis sightings have been more common than third-party underride guards.

"I know of no company that even intends to get involved in the guard manufacturing business," a trailer manufacturer declares. "Any guard manufacturer must test the product on various trailer configurations. He will be required to supply mounting instructions that must be followed if the certification is to stand. I have asked people whose current products would make manufacturing a guard viable. They won't touch it. An underride guard is a product liability magnet."

At least one company, however, is contemplating offering an underride guard that trailer manufacturers can install. BUCO Systems Inc of Fresno, California, has completed extensive development work in crash impact technology, including truck-mounted devices designed to improve safety when cars impact trucks from behind.

"We have more than $2 million invested in research and software written specifically for vehicle crash analysis," a company spokesman says. "To produce a guard that meets the parameters defined in FMVSS 223 and FMVSS 224 should fall well within our capabilities."

BUCO also is developing attachable impact devices that will supplement existing systems. Manufacturing facilities for both the trailer-mounted rear impact guards and the attachable supplemental devices also are in the works. The company is located at 5528 North Palm, Suite 122, Fresno CA 93704. The phone number is (209) 436-8901.

BUCO plans to have product ready for market by the end of this year. If so, many trailer manufacturers just might be interested.

"We have been hoping some big trailer manufacturer or someone would have underride guards to sell," a small trailer manufacturer said. "We have to buy one-we don't have the resources to design and test guards ourselves."

The method for testing the strength requirements of a rear impact guard is nothing new. The Truck Trailer Manufacturers Association published a recommended practice on the subject in 1994, before energy-absorption requirements were added to the new regulation.

Part of a recommended practice titled "Rear Impact Guard and Protection," the test procedures are described in detail. According to the TTMA:

*The guard should be attached to a rigid test stand in a manner that represents the way it would be installed on a trailer.

*Force is to be applied to the guard using a rigid steel surface measuring 8" x 8". Each edge of the contact surface is to have a radius ranging from 5/32" to 1/4".

*The contact surface of the loading device should be centered on the test point.

*Subject the guard to the specified force: 11,240 lb on the curbside, roadside, or center points of the guard's horizontal member; 22,480 lb where the horizontal member is attached to the vertical member. Each of these forces is to be applied separately-not simultaneously. The force must be applied at a constant rate.

*The loading device must not rotate.

*When the specified load is reached, measure the distance that the center point of the loading device contact surface has traveled forward from its initial point of contact with the guard.