THE HEAVY DUTY BRAKE MANUFACTURERS COUNCIL (HDBMC) supports proposed rulemaking by the National Highway Traffic Safety Administration (NHTSA) to reduce the stopping distance for truck tractors equipped with air brakes by 20% to 30%, but questions that not enough is known about the impact.
“The point we made in our response is that we are supporting a 25% reduction,” says HDBMC chairman Paul Johnston, senior director of ArvinMeritor's North American Foundation Brake Business. “But we are concerned about the degree of change and what the impact will be on the normal operating condition of the vehicle, not just straight-ahead stopping performance. We feel the industry, including ourselves, has not necessarily done enough homework to have evaluated a 20%, 25%, or even 30% reduction, and what that impact will be.”
HDBMC, a technical council of the Heavy Duty Manufacturers Association (HDMA) founded in the late 1970s, consists of top engineering representatives from 14 braking-system manufacturers and works closely with government and other industry organizations on design standards and regulatory and safety issues.
According to Federal Motor Vehicle Safety Standards (FMVSS) No. 121, pneumatically braked truck tractors are required to stop from 60 mph in 355 feet at GVWR, compared to the FMVSS No. 135 requirement for passenger cars of 216 feet. NHTSA believes that improving the discrepancy in stopping distances is critical in reducing heavy-truck-related fatalities.
In its Notice of Proposed Rulemaking (NPRM) in the Federal Register on December 15, 2005, NHTSA says it believes that “by pursuing rulemaking to improve stopping distance performance, truck manufacturers will re-examine their specifications for brake components and make improvements, particularly on the steer axle brakes, and in other areas as well. In this industry, brake systems are installed according to specifications provided by truck purchasers/trucking fleets. NHTSA's preliminary regulatory impact analysis shows that enhanced brake system specifications will have net cost savings for truck operators after considering property damage savings. However, truck operators do not have this cost-saving information and only a few fleets are purchasing these improved systems.”
It concludes that “progress towards improved brake systems is impeded because truck operators are cost sensitive to the initial purchase price and they are reluctant to add different types and sizes of brake components to their specifications. Although truck manufacturers offer improved drum brakes and are introducing air disc brakes, very few fleets are purchasing them. Generally, the trend is to stay with the same brakes that have been used for many decades.”
Meeting the reductions
HDBMC agrees with NHTSA that truck tractors can achieve the proposed stopping-distance reductions with existing brake technologies.
“We believe either a drum brake or disc brake will meet the intent of the rulemaking,” Johnston says. “We collectively feel we have, or will have, product available to meet those needs. It's how it's implemented as a system at the OEM level as well as fleet level that has us more concerned. The OEMs have to address or will address total vehicle changes needed for a 20%, 25%, or 30% reduction in stopping distance. Each level of reduction has a different resulting change required by OEMs.”
Says HDBMC vice chairman Jim Szudy, engineering manager for Bendix Commercial Vehicle Systems, “The front-axle brakes will probably have not only an increase in torque, but also better temperature and in-stop fade characteristics. Therefore, not only will some of the torques be increased, but also because of the larger brake, the fade will be decreased during a stop because of the better thermal capacity of the brake. In general, in terms of drums, we've been looking at 16½×5 instead of 15×4.”
Immediate past chairman Randy Petresh, director of engineering for Haldex Brake Product Corp, says HDBMC's concern is the issue of mixing technologies.
“Regardless of what combination you have, you have the potential for imbalance,” he says. “If you just go with discs on a steer axle, you have the minimal effect if you just change the steer axle. The biggest concern is with an all-disc tractor or an all-disc trailer. The problem is the difference in performance at elevated temperatures or extreme conditions where the disc-brake unit could be doing more of the braking effort for the total combination. That will generate customer dissatisfaction such as early wearouts and maintenance issues.”
“As well as potential stability issues, which we haven't fully evaluated,” Szudy adds.
NHTSA estimates that 3% of the current truck tractors would comply with a 30% improved brake performance, and the benefits of a 30% improvement in stopping distance are estimated to be a reduction of 257 fatalities and prevention of 284 Abbreviated Injury Severity (AIS) 3-5 injuries among occupants in truck trailer crashes.
It also estimates that 34% of the current truck tractors would comply with a 20% improvement in the stopping-distance requirements distance without any modification, and a 20% reduction in stopping distance would save 104 fatalities and prevent 120 AIS 3-5 injuries among occupants in truck trailer crashes.
NHTSA says potential compliance costs for the proposed 30% and 20% stopping-reduction requirements vary considerably and are dependent upon the types of the brake systems chosen by the manufacturers.
“Limited testing showed that both larger S-cam drum brakes and disc brakes at all wheel positions could meet the proposed 30% and 20% reduction in stopping distance. Given the current level of compliance, the average incremental cost per truck tractor would be $153 for larger S-cam drum brakes and $1,308 for disc brakes for the 30 percent reduction in stopping distance and $108 for larger S-cam drum brakes and $914 for disc brakes for the 20% reduction in stopping distance. We estimate that the total incremental cost for the 30% reduction would range from $20 million to $170 million dollars and that the total cost for the 20% reduction would range from $14 million to $119 million dollars.
“However, when the prevention of property damage and equivalent lives saved are considered (at a 3% discount rate) the 30% reduction would result in a net benefit ranging from $994 million to $1,144 million. The 20% reduction would result in a net benefit ranging from $320 million to $425 million.
“These costs and benefits were based on analyses of tests using vehicles that the agency believes to be representative of a majority of the market. We recognize that there may be vehicle configurations for which the cost of compliance may be higher.”
NHTSA says it understands that improvements in truck tractor stopping-distance performance may involve more than simply increasing the power of foundation brakes, “as changes might be required to suspensions and frames, etc, to handle the higher braking torque without decreasing vehicle durability and safety.”
However, NHTSA believes that two years of lead time after a final rule is issued would be adequate lead time for manufacturers to comply with a reduction in stopping distance in the proposed range.
“Given that vehicles tested by the agency and industry were able to comply with the proposed reductions without modifications other than to the foundation brakes, we believe that this is adequate lead time,” NHTSA says.
NHTSA, which closed the comment stage on April 14, is expected to issue its Final Rule in May 2007.
In its April 13 response to NHTSA, HDBMC submitted these points:
“HDBMC supports the agency's efforts to advance heavy-duty vehicle safety and seeks a realistic and effective technique for improving and reducing stopping distance on standard truck tractors on the national highways.”
“NHTSA should target the current stopping- distance performance requirements on those typical three-axle truck tractors … We believe, in looking at independent studies and research done by TMA (Truck Manufacturers Association) and others that this population of vehicles represents a significant and meaningful opportunity to reduce stopping distances that satisfy the intent of the NPRM.”
“We continue to support and actively participate as much as we can in a collaborative vehicle/government/industry/supplier-based effort to further examine stopping-distance performance on all vehicle types, including ‘non-typical’ truck tractors, straight trucks, and trailers, going forward with this rulemaking activity. Clearly we feel we have the knowledge, the resources, the products, and the ability to support both the government as well as OEM and fleet customers to do this collaborative research testing and that we really encourage everyone to continue with testing in parallel with the final rulemaking activities we're now in.”
“Regarding implementation, we have recommended to NHTSA that they should keep the current EPA emissions standard in 2007 as well as in 2010 inline as they set the implementation date of this stopping-distance rulemaking and we recommended to them this be done with the intent of implementing these regulations on vehicles no earlier than 2008 and as early as possible in 2009 at the latest in order to meet the 2007 and 2010 tasks that our customers and fleets have to deal with.”
“Relative to our primary recommendation regarding the tractor configuration, there are other types of truck tractor configurations that are not part of the recommendation and that would concern configurations like severe-service tractors with higher GVWR ratings and multiple axles, so we've indicated other factors that affect performance of these vehicles such as tire-adhesion characteristics, vehicle dynamics, and vehicle configurations related to wheelbase and center of gravity would need to be closely examined in much more detail than we have been able to do to date and therefore would require a lot more testing.”
“As we in the industry know, the burnish procedure as it relates to conditioning of the brakes to measure performance is a very critical part of the process. Currently the standard (FMVSS) 121 has a burnish procedure in there and we're concerned this may be too restrictive down the road or may not provide the latitude of optimizing the systems going forward, so we've asked that the agency examine the effects of burnish on stopping-distance performance.”
“Table 2 in the NPRM talks about stopping distance at the various speeds. We've focused primarily on 60 mph stopping distances, but when you calculate backward for the lower speeds, the driver reaction time becomes a larger and larger factor. We don't believe the agency has considered that reaction time carefully enough and have asked them to reanalyze the values in that chart to look at that reaction time as part of the total stopping distance.”
“Due to the increase percentage of braking contributed by the truck tractor in order to achieve a shorter stopping distance, brake system balance will need to be further evaluated. That means that the front-axle torque looks to be the axle where the torque needs to be increased due to the weight shift. Therefore, the higher torque will increase the percentage of the total combination vehicle braking that the tractor will be doing. HDBMC is saying that although this is not an action taken by NHTSA, it is an action the industry needs to look at it in terms of how it affects, for example, maintenance costs.”
“No changes to the dynamometer procedure should be made at this time. Both the front axle, which is only regulated by the brake section of (FMVSS) 121, and the tractor drive axles, which also are regulated by brake power and the brake-recovery tests, are minimum performance requirements and therefore do not limit the amount of torque the brake can put out. Therefore, because these are minimums, the vehicle manufacturers will not be limited in their ability to pick or use higher torque brakes on their vehicles in order to meet the requirement.”
“It is important that in-service braking performance be maintained during the life of the vehicle to fully realize the benefits of the proposed changes. The DOT should further address how to ensure that new vehicle performance is maintained. The effectiveness of the new regulation will be measured over time. And over time, if you start changing the configuration of the vehicle, the effectiveness of the regulation may not be fully obtained. Therefore, HDBMC believes that maintenance, particularly proper lining, should be chosen in order to obtain this shorter stopping-distance performance.”