Test procedures

FMVSS 213 Testing

Given the high level of occupant protection provided by current child restraints in all types of crashes, people are often surprised to find that the testing requirements as defined in the applicable federal rule, FMVSS 213, primarily focus on their performance in frontal crashes at one severity level (CFR, FMVSS 213). In addition, though vehicle seats, LATCH anchorage locations, and seatbelt geometry vary widely in vehicles, child restraints are tested on a generic, soft, flat, bench seat using either a single set of belt anchorages or LATCH anchorages. (NHTSA announced a planned update of the bench with more realistic characteristics in November 2020). Child restraints are not crash tested in real vehicles, but tested using a sled that simulates the acceleration seen in a crash with a 30 mi/hr (48 km/hr) change in velocity. Sled tests are used because they are more repeatable and less expensive. At first glance, a 30-mi/hr (48 km/hr) test may not seem very severe, but 30 mi/hr (48 km/hr) refers to the change in velocity, not the velocity at the time of the crash, and the crash conditions used are more severe than 96% of actual frontal crashes in the United States.

When evaluating the dynamic safety performance of a child restraint, requirements vary with the type of restraint. For a car bed, the primary criterion is that the harness must keep the newborn size dummy in the restraint. For rear-facing restraints, a restraint will pass if the surface supporting the crash dummy’s back does not rotate forward beyond an angle of 70°, the head and chest of the dummy stay in the restraint, and the acceleration characteristics for the dummy’s head and chest do not exceed prescribed thresholds. For forward-facing restraints and booster seats, the dummy’s head must not move forward past a point 720 mm (28.4 inches) from a seat reference point when tested with a tether or 813 mm (32 inches) when tested without a tether; in either condition, the knees must not pass a point 915 mm (36 inches) away. In addition, there are limits on head and chest acceleration-based measures. Unfortunately, better scores on the head injury criteria can usually be achieved by allowing more head excursion, although keeping the head from moving further forward corresponds to preventing the most common real-world head injury mechanism of the child’s head striking something in the vehicle (Bohman et al. 2011). Other 213 requirements focus on webbing strength, width, and abrasion resistance, flammability of the components, buckle release characteristics, and padding requirements. Tests are also performed to determine whether the child would stay within the restraint when it is inverted.

FMVSS 225

Requirements for LATCH hardware in vehicles are specified in FMVSS 225 (CFR FMVSS 225). Most vehicles have the minimum required LATCH hardware where top tether anchorages are provided in three seating positions and lower anchorages are provided in two seating positions. The regulation defines zones for locating the lower and tether anchorages, as well as quasi-static (or slow loading) testing procedures for evaluating the strength of the lower and top tether anchorages. Other requirements for lower anchorages include specifications for the size and spacing of the anchor bars that comprise the lower anchorages, and requirements for how a child restraint fixture must fit in the vehicle when attached to the lower anchorages.

In 2015, the Insurance Institute for Highway Safety (IIHS) added a LATCH ease-of-use rating system to its vehicle safety evaluations. The procedures used are based on research showing that lower anchors with shallower depth, lower required attachment force, and greater space around the anchors resulted in fewer CRS installation errors than vehicles where lower anchors did not exhibit these characteristics (Jermakian et al. 2014, Klinich et al. 2013a, 2013b, 2014). This consumer information program has led to improvements in the LATCH usability.

Side impact testing

Vehicle-to-vehicle side impact events are often described based on the occupant’s position relative to the striking vehicle. If the occupant is on the opposite side of the vehicle from the striking object it is called the “far-side” impact condition and a seat belt can play an important role in the outcome by limiting the possibility of occupant contact. When the occupant is positioned on the side of the vehicle closest to the striking vehicle it is called a “near-side” impact event and injuries are often caused by direct loading between the striking object and the occupant. In near-side events, use of the seat belt is less of a factor in the crash injury outcomes. Near-side impacts are most injurious, and the occupant motions involve the child restraint moving toward the door as the door is intruding from the striking vehicle. US child restraint products currently do not have to be tested under side impact loading conditions. However, many child restraint manufacturers advertise that they have tested their products in side impact using internal test procedures, although details of the exact procedures are not described. Side impact tests are generally conducted with dummies that are designed for side impact evaluation. In addition, the simulated side impact crash is run at a lower change in velocity than frontal impact testing to reflect the typical crash severity in the field.

Many different strategies have been proposed for testing child restraints in side impact to approximate the loading conditions seen in a vehicle. Child restraint manufacturers likely use some combination of these tests. Methods include:

• Repositioning the bench used for frontal impact testing and decelerating the child restraint laterally. This represents the loading that a child restraint would undergo in a far-side crash. This type of testing does not represent the most injurious side impact loading, but can demonstrate how well the attachment system keeps the child restraint from moving laterally and how well the dummy’s head is contained within the restraint.

• Lateral loading into a fixed rigid wall. The main difference between this method and the previous one is that the test fixture includes a rigid plate mounted at the end of the seating bench. This testing method is used in Australian regulations (Standard AS/NZS 1754). In addition to demonstrating the ability to prevent lateral movement and contain the dummy’s head, this method allows a rough assessment of head injury potential from contacting a vehicle surface.

• Lateral loading into a rotating door. This approach, considered for European testing, was thought to provide a way of approximating intrusion. The characteristics of the door have a significant effect on the loading. It was difficult to achieve consensus on what the door characteristics should be as the design of vehicles has changed over time in response to vehicle side-impact requirements.

• Simulated door intrusion. This strategy propels a simulated door into the side of a fixed child restraint. This approach captures most of the kinematics of a near-side crash except for the initial movement of the child restraint towards the intruding door. An example of this approach is the European Union regulation that uses a moving sled to propel the child restraint into a padded fixed door and the side impact test fixture developed by Dorel and Kettering University.

• Simulated door intrusion including child restraint motion. Takata Corporation developed a side impact sled test method that simulates the door intrusion typical of a crash with a near-side occupant in a child restraint system. The method employs a base structure that simulates the vehicle door and a separate vehicle seat that slides on rails and moves into the door structure during the crash event. Honeycomb aluminum is positioned between the two elements to simulate the crush of the vehicle structure. The door structure is padded to simulate the compliance of a vehicle door. The method can be used to run a pure side impact or a side impact crash with a frontal deceleration component by adjusting the mounting angle of the entire buck relative to the primary direction of sled movement. (Sullivan and Louden 2009, Sullivan et al. 2011). NHTSA issued a notice of proposed rulemaking in 2014 announcing plans to test CRS for children under 40 lb using methods based on this research, but the requirements have not yet been adopted.

While the idea of testing child restraints in side impact has merit, design changes in response to side impact testing may have unintended consequences. If child restraints become wider to accommodate padding or larger sidewings, they may be more difficult to install with a child restraint in an adjacent seating position. Restraints may also become heavier and stiffer, possibly posing an injury risk to adjacent occupants. In addition, testing procedures evaluate injury risk by measuring lateral head excursion, and most rear-facing restraints have higher values than forward-facing seats even though they are be safer in crashes. Comparison of values may encourage caregivers to inappropriately shift to forward-facing restraints prematurely. Because belt-positioning boosters do not actually restrain a child, but position them so they can be better protected by the vehicle seatbelts and vehicle components such as curtain airbags and energy-absorbing structures, it would not be reasonable to test boosters under side impact conditions.

Vehicle testing

In addition to testing of child restraints, vehicles must meet regulatory requirements that pertain to protection of child occupants. Vehicle manufacturers perform a series of tests to ensure that frontal airbags do not deploy at injurious levels when a child occupant is in the right-front seating position, including when they are “out-of-position” and close to the airbag module (CFR FMVSS 208). Vehicle manufacturers also perform voluntary testing to check that side airbags do not pose a danger to children (Side Airbag Working Group 2003). FMVSS 201 defines tests for evaluating the injury potential if occupants contact interior structures of the vehicle, such as the roof and B-pillars (CFR FMVSS 201). While children benefit from the interior padding and energy-absorbing structures that result from these requirements, the requirements do not apply to many of the structures in the rear seat that are commonly contacted by child occupants during crashes because the regulation primarily addresses interior points at or above the window sill (Arbogast et al. 2012, Jermakian et al. 2007). FMVSS 214, which evaluates the safety of vehicles in side impacts using adult-sized crash dummies, also benefits child occupants (CFR FMVSS 214).

Child restraints are not currently tested in vehicle crash tests for regulatory purposes. However, vehicle designs developed to improve safety for adult occupants in regulatory and consumer testing may benefit child occupants as well. Research has been conducted using child restraints and pediatric dummies in a number of test programs that have identified possible issues with child restraint performance in severe crashes (Park et al. 2011, Tylko 2011). These results have led to additional research programs to identify methods of improving the safety of the rear seating compartment for the child occupants who primarily sit there (Hu et al. 2011, Klinich et al. 2008, Klinich et al. 2011,Reed et al. 2008).

9-27-21