NHTSA Rear Guard NPRM legalizes current guards for the next twenty years?

NHTSA is proposing to adopt requirements of the Canada Motor Vehicle Safety Standard (CMVSS) for underride guards (CMVSS No. 223, “Rear impact guards,”) that became effective in 2007.

NHTSA is stealing a 2007 safety regulation from another country to apply to U.S. trailers in 2018 and beyond! We are looking at adopting an 11 year old regulation during the time of the swiftest change in automotive technology including safety in history. We cannot afford to do our own research and write our own regulations.

The CMVSS No. 223 requirements are intended to provide rear impact guards with sufficient strength and energy absorption capability to protect occupants of compact and subcompact passenger cars impacting the rear of trailers at 56 km/h (35 mph).

We recognize, however, that benefits may accrue from underride crashes at speeds higher than 56 km/h (35 mph), if, e.g., a vehicle’s guard exceeded the minimum performance requirements of the FMVSS. NHTSA requests information that would assist the agency in quantifying the possible benefits of CMVSS No. 223 rear impact guards in crashes with speeds higher than 56 km/h (35 mph).

About 26 percent of fatal light vehicle crashes into the rear of trailers is at speeds 56 km/h (35 mph) or less, this means 74% of fatal light vehicle crashes are at speeds exceeding 56 km/h (35 mph). This means that NHTSA for the next twenty years or until around 2040 will not try to save 3/4 of fatal victims.

MUARC tested energy-absorbing guards to 75 km/h or 47 mph in the early 1990’s and the Impact Project tested energy-absorbing guards to 40 mph full and offset with computer models showing performance possible at 50 mph and more.

MUARC Guard PicMUARC Monash University Australia energy absorbing guard design
Strong energy absorbing struts to outside edge for offset crashes



UNICAMP CRASH TEST PICUNICAMP Impact Project in Brazil energy absorbing guard test
Angled high strength reinforcing struts to outside edge


“The size of an energy-absorbing truck front structure directly correlates to the survivable closing speed between car and truck in head-on collisions (e.g. 75 km/h survivable closing speed requires a 400 mm long energy-absorbing structure, 90 km/h (56 mph), requires 800 mm).” From Volvo Report

NHTSA Study: ” A study by Minahan and O’Day of fatal car-truck accidents in Michigan and Texas found evidence of underride in 90 percent of rear-end impacts and 70 percent of side impacts. Underride was found typically to occur at night on straight rural roads. Impact speeds were generally greater than 30 mph. The authors characterized this type of crash as a “surprise event” in which a passenger vehicle came upon a slower or stopped truck unexpectedly.”

VC-COMPAT Project The analysis revealed that approximately 57 % of the fatalities and 67 % of seriously injured could be prevented from their injures due to improved rear underrun protection systems (RUPS).

VC-COMPAT: “Plans are underway to extend the front of the truck 300mm to 500mm or more to create a crash zone or deformable soft nose that would absorb crash energy and might reduce serious injuries and fatalities another 10% from the current standard on trucks with energy-absorbing guards, and survivable speeds would be increased to 80-90kph (56 mph).”

NHTSA refuses to crash test at real world speeds including highway speeds to keep this information from the public to encourage uninformed adoption of these corporate preferred cheap and low speed guard standards.

Based on information from the Truck Trailer Manufacturers Association (TTMA), NHTSA estimates that 93 percent of new trailers sold in the U.S. subject to FMVSS Nos. 223 and 224 are already designed to comply with CMVSS No. 223. The agency estimates that about one life and three serious injuries would be saved annually by requiring all applicable trailers to be equipped with CMVSS No. 223 compliant guards.

The NPRM intends to upgrade the Standard as basically existed in 1996, 2018 is suggested as the final date of implementation. It takes twenty to thirty years to agree on a new regulation, by the time 2018 rolls around we would probably see 98 % of trucks on the road voluntarily meeting the Canadian Standard due to crash testing guards at IIHS providing some pressure for guard design improvement. This means we will be legalizing 98 % of current guards for the next twenty plus years with no technological improvement to the guards already on the roadway today! We will have 1950’s technology in 2040!

Further, an evaluation of trailers manufactured in 1998 and later in the 2008-2009 TIFA data files from UMTRI showed that the average ground clearance of rear impact guards for newer (MY 1998+) trailer models was 457 mm (18 inches).

Some trailers may have the rear axle further forward to improve maneuverability of the trailer. NHTSA believes that, for such trailers, rear impact guards that are lower than 560 mm (22 inches) may scrape and snag with the ground and get damaged.

NHTSA plans on keeping guards at 22 inches discounting numerous studies showing lower guard heights improve injury and fatality outcomes. NHTSA hides all favorable information and studies from the public. Average guard height is already 18 inches or lower. In violation of Vision Zero NHTSA places possible maneuverability over saving lives.

The guard bottom must be close to the road to align at the height of most car bumpers, around 400 mm or 16 inches. The bumper must be engaged to properly interact with car safety features such as crush zones which are designed to absorb crash energy. If the guard is not low enough the car can penetrate below the guard and create the wedge effect (See Below) lifting the trailer causing crush zone features of the car to not engage and sending the hard bottom edge of the trailer towards the windshield and car occupants.

Penn State simulated car-truck crashes with varying guard heights

400 mm = 16 inches   600 mm = about 23 inches

MUARC recommends 400 mm height or about 16 inches

Requiring that the guard be tested when attached to the trailer would be an unnecessary and significant cost burden for the manufacturers, especially for small trailer manufacturers with low sales volumes.

Violates Vision Zero reducing fatalities.

Guards can break off of trailers during a crash due to the massive force involved. Attachment hardware such as bolts must be extra thick and strong, attachment points such as the trailer frame must also withstand tremendous forces and if not strong enough the trailer frame should be required to be reinforced in the standard. Guards should be tested on the trailer so attachment failure which is common can be decreased.

IIHS states that ideally, FMVSS No. 223 should require guards to be certified while attached to complete trailers, and that at a minimum, guards should be tested while attached to sections of the trailer rear that include all the major structural components and that are constrained such that the load paths near the guard are not changed.

The Manac rear impact guard prevented PCI in 56 km/h (35 mph) crash tests with full overlap, 50 percent and 30 percent overlap of the Malibu.

Manac guards are heavier at 307 pounds. Improved guards will not be the norm due to higher weights and costs for little improvement. History shows minimum compliance, not maximum as with the Manac guards. We should see about 30 mph performance for minimum compliance with poor extreme offset performance.

We have tentatively decided not to require used trailers be retrofitted with CMVSS No. 223 compliant rear impact guards. Our analysis indicates such a retrofitting requirement would be very costly without sufficient safety benefits.

MUARC in Australia recommended an extra angled brace attached to the outside edge of the guard running to the horizontal trailer frame in their study of rear guards in the 1990’s. The Impact Project in Brazil also incorporated this outside angled brace and recommendation in their guard designs and recommendations. These braces could be added to older guard designs to improve offset impact performance and enhance full impact strength. Using new high strength aluminum alloys these braces could be added as zero cost as part of normal maintenance budget operations, with low cost, and low weight.

While 20 percent of fatal light vehicle impacts into the rear of trailers are wheels back trailers, they only represent 8 percent of those fatal crashes with PCI into the rear of trucks and 30 trailers.

Wheels back trailers are now exempt from guard standards but modern cars require a flat surface to interact with their safety systems. Tires are hard surfaces and present an uneven surface hazard that can be mitigated with the flat surface and proper height and energy absorbing features of an properly designed underride guard. NHTSA Study: “Wide-base singles may become more widespread to improve the fuel economy of the truck population. Wide-base singles present a larger gap for smaller, narrower light vehicles, which in turn brings the wheels-back exemption into question.”

In 2010, NHTSA published the results of a study, analyzing several data sources, to determine the effectiveness of trailer rear impact guards compliant with FMVSS Nos. 223 and 224 in preventing fatalities and serious injuries.5 The agency’s analysis of the Fatality Analysis Reporting System (FARS) could not establish a nationwide downward trend in fatalities to passenger vehicle occupants in impacts with the rear of trailers subsequent to the implementation of FMVSS Nos. 223 and 224.

Previous legalization of guards already on the road by NHTSA did not improve safety contrary to NHTSA claims which were disputed by all non-industry parties. In twenty years, we fear a similar outcome from legalizing guards on the road today.

We propose to replace the current definition of “rear extremity” in FMVSS No. 224 with that specified in CMVSS No. 223. The change is intended to ensure that aerodynamic fairings are located within a certain safe zone at the rear of the trailer. Aerodynamic fairings on the rear of trailers, also known as “boat tails,” are rear-mounted panels on trailers that reduce aerodynamic drag and fuel consumption.

Actually, common sense. We would recommend extending guards for high speed performance.

The average cost of a Canadian compliant rear impact guard is $492, which is $229 more than an FMVSS No. 224 compliant guard.

As shown in Table 10, upgrading from the FMVSS No. 224 compliant guard to the CMVSS No. 223 compliant guard would add an average incremental weight of 48.9 lb to the trailer, thereby reducing the overall fuel economy during the lifetime of the trailer. The incremental increase in lifetime fuel cost for a 48.9 lb weight increase of a trailer was estimated to be $1,042.2 and $927.7 discounted at 3 percent and 7 percent, respectively.

Excludes information on new light weight aluminum alloys purported to be low cost and as strong as titanium. Does not discuss weight and viability of new high strength plastics. Does not examine low cost imports from China which are increasingly available. NHTSA costs are outdated from relatively small suppliers. Fully energy absorbing guards in quantity should cost in the $500 range.

VC-Compat Improved Rear Underride Guard Costs in EU: Current RUP devices cost 100 € – 200 € (Approx. $134 – $268) per vehicle. Additional costs ranging from 20 € to 100 € (Approx. $27 to $134) are estimated for ‘low profile’ improved RUP, while additional costs for more complex folding devices may exceed 200 € (Approx. $268) per vehicle.

Upper Great Plains Transportation Institute at NDSU: “Cost-benefit analysis shows that the rear-guard safety equipment has injury severity benefits that far outweigh equipment cost. Given a 10 percent reduction in injury severity attributed to the rear-guard devices on agricultural trucks, in the relevant crash population, the benefit is esti-mated to be $14.4 million over the seven-year depreciable life of a truck. Total equipment and maintenance cost for the North Dakota agricultural truck fleet is estimated to be $8.1 million. An estimated safety benefit of $1.76 is generated from each dollar spent on rear guards for North Dakota’s agricultural truck fleet.”

As such, NHTSA does not intend that this proposed rule would preempt state tort law that would effectively impose a higher standard on motor vehicle manufacturers than that established by today’s proposed rule. Establishment of a higher standard by means of State tort law would not conflict with the minimum standard proposed here. Without any conflict, there could not be any implied preemption of a State common law tort cause of action.

Real world cases show these laws are used to exclude evidence against trucking companies and make lawsuits more expensive for victims. Strict Liability is almost impossible.

CMVSS No. 223 permits an option that a rear impact guard does not have to meet energy absorption requirements if it is able to resist 700,000 N of force using the distributed load application device without deflecting more than 125 mm.

Modern cars can survive crashes into solid walls at more than 40 mph including in modest offset impacts. You basically allow the cars safety systems to absorb all of the crash energy and build the guard very strong and rigid to prevent PCI.

VC-Compat: “the energy absorbing capability and capacity of passenger car front structures has improved to such an extend that impact speeds up to 64 – 75 km/h (Approx. 40 mph to 47 mph) may well be survivable for passenger car occupants in collision with rigid FUPs.“

If you must give up on high speed energy absorbing guards that will save more lives and prevent more injuries for the same cost then this might make sense.

However, the full overlap crash test results indicate that trailers that have the main vertical supports for the guard more outboard may not perform as well in full overlap crashes as trailers that have the vertical supports more inboard for crash speeds greater than 56 km/h (35 mph). Since full and 50 percent overlap crashes are more frequent than low overlap (30 percent or less) crashes, and since most fatal light vehicle impacts into the rear of trailers are at speeds greater than 56 km/h (35 mph), such guard designs may reduce protection against PCI in higher speed full and 50 percent overlap crashes.

NHTSA in 1992 successfully tested aluminum honeycomb guards that deflected cars at high speed in severe offset crashes.

Offset crashes can kill in even a few inches of overlap with the trailer. It is common to have guards not extend to the outside edges of the trailer, when the car hits just a few inches from the outside edge it can completely miss the outside edge of the guard and at a slight angle can underride the trailer up to five feet until it contacts tires with catastrophic results. These offset from center crashes are common and the force of the impact can be concentrated in the outside inches of the guard away from the reinforcing struts that hold the guard bar to the trailer. It is important to have the guard extend all of the way to the edge of the trailer with angled high strength reinforcing struts close to the ends of the guard, probably not more than 6 to 8 inches from the trailer edge. Moving the P1 force test location further out to the edge of the guard such as IIHS recommends will help to guarantee the ends of the guard are strong for these offset crashes. We must require better bracing than vertical struts provide!

UNICAMP CRASH TEST PICUNICAMP Impact Project in Brazil energy absorbing guard test
Angled high strength reinforcing struts to outside edge


The Canadian standard is only effective to about 30 mph with minimum guards in offset impacts with a single guard manufacturer tested successfully to 35 mph in offset tests. If we harmonized to the weak Canadian Standard most trucks and trailers will only meet the minimum requirements and we would be stuck for twenty years with an 30 mph standard that protects only a quarter of victims. Increasing energy absorption requirements to 50 kj minimum would force adoption of energy absorbing guards that we feel strongly will save lives at 50 mph and more with little extra weight due to modern materials and for similar cost. NHTSA must begin a robust crash testing program for guards to enhance safety design and encourage adoption of better performing designs.

Recommended Reading:

Improved Crashworthy Designs for Truck Underride Guards in PDF

VC-Compat Final Technical Report.pdf

TARS Research Centre submission NHTSA Rulemaking SUTs PDF

American Standards Rear Guards – Comments Luis Otto

Tomossoni NHTSA Crash tests 1992

The Underride Network supports a high-speed standard such as recommendations from MUARC in Australia would present.


1.    Barrier test Forces:

P1 (outer edge)   P2 (off centre)   P3 (centre)

              200 kN          200 kN          100 kN

2.    Barrier height: 400mm

3.    Barrier width: Within 100mm of the outer frame of the rear of the truck

4.    Energy absorption: 50kJ minimum