Getting Ready for Underride
Oct 1, 1997 12:00 PM
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. 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.
Most petroleum transports will be exempt from the underride regulation, according to Ed Mansell, director of engineering at Polar Tank Trailer Inc. However, underride bumpers will be required in some instances.
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.
"Polar Tank Trailer has been installing rear impact guards, in compliance with TTMA's Recommended Practice, for the past three years as standard equipment," Mansell says. "All of our designs have been physically tested for the strength requirements and comply with the recommended practice.
"As you know, the latest requirement is to determine the energy absorbed for deforming a rear impact guard from zero inches to five inches. We are planning on having all of our rear impact guards tested in compliance with the new requirement by the end of October 1997. Based on finite element analysis and previous testing, we do not anticipate that any major design changes will be needed.
"The real burden is having to invest in sophisticated equipment that is unnecessary. Like other manufacturers, we are asking NHTSA to drop the requirement for a displacement rate of 1.0 to 1.5 mm per second. This requirement is burdensome and has no relevance as it relates to "the calculation of energy absorption" as defined in 49 CFR 571.223 Section S6.6 (c) or the measurement of the guard strength as defined in 49 CFR 571.223 Section S5.2.1.
"Under the current rule, a trailer manufacturer could easily spend $10,000 to $15,000 on testing equipment. We could get by with less test equipment if the displacement rate requirement was dropped."
John Cannon, vice-president of engineering at Brenner Tank Inc, says that tank trailer manufacturers are in the position of installing rear underride bumpers that have not been fully tested. "We're still waiting for a variety of factors to be cleared up in the rule," he adds. "TTMA has asked for a nine-month delay that would push the implementation date back.
The current rule leaves little room for design innovation, according to Jack Rademacher, chief engineer at Bar-Bel Fabricating Co Inc. "We're still hoping for changes in the rule, especially the sections that apply to testing," he says. "In many ways, the rule is incomplete. For instance, accident damage is not addressed. There are no repair or replacement requirements. Strength requirements just apply to new manufactured trailers."
Smaller Manufacturers Struggle Tank manufacturers interviewed for this article generally agreed that smaller builders face the biggest challenges in complying with the underride regulations. The smaller tank trailer manufacturers may have a very difficult time meeting the testing requirements unless changes are made.
Many of the small builders are still trying to decide how they are going to comply. "We haven't even addressed underride bumpers yet," says Trevor Bristol, sales engineer for Marsh Industrial Services Inc. "Bumpers on our vacuum trailers are already rugged enough and low enough that we may be in good shape without a lot of design changes."
The new underride bumpers have a 22-inch ground height limit. In contrast, the current "DOT bumper" provided 30 inches of ground clearance.
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.
Most underride bumpers will add 50 to 100 pounds to a tank trailer, and they will cost between $100 and $200. The cost will depend on whether the bumper is fabricated from stainless steel, carbon steel, or aluminum. In all likelihood, the cost will be rolled into general price increases at the end of the year.
Manufacturers stress that buyers will not be hit with any big jump in prices due to the underride requirement. "This is not an opportunity to jack up our prices," one manufacturer says.
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."
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