Child Restraint/Vehicle Compatibility

Much of my recent research related to child passenger safety has focused on improving child restraint and vehicle compatibility. Several studies performed for the Insurance Institute for Highway Safety involved volunteer testing to evaluate vehicle features related to the usability of LATCH (lower anchors and tethers for children) system used to secure child restraints in vehicles. This research was the basis for new vehicle ratings on LATCH usability first published by the IIHS in June 2016 as part of their consumer information program website. In addition, the National Highway Traffic Safety Administration issued a Notice of Proposed Rulemaking to modify FMVSS No. 225 that specifies new requirements for lower anchor depth, attachment force, and clearance angle based on these UMTRI studies.

Other projects in this area have led to the development of fit envelopes to increase compatibility between child restraints and vehicles. Adapting a model used by the International Standards Organization, we analyzed the shape of a range of recent child restraint models and documented their installed position in ten late model vehicles. Size envelopes representing the installed position of small, medium, and large rear-facing and forward-facing child restraints have been developed and are being evaluated by NHTSA for inclusion in their consumer information program. The intent is that if child restraint manufacturers design their products so they fit within the envelope, and vehicle manufacturers design their rear seat to accommodate the envelopes, it will lead to greater compatibility between the geometry of child restraints and vehicles.

Child Restraint Testing Procedures

The most recent version of FMVSS No. 213 that went into effect in February 2014 includes seating procedures and injury criteria for use in evaluating belt-positioning booster seats that were developed at UMTRI. The new procedures seat the ATD in a manner closer to that selected by child volunteers of similar sizes; the belt tension is also now set to a more realistic level. These changes will allow booster seat designs to be assessed in a more realistic condition that is closer to how they are used in vehicles. Ongoing work to improve the evaluation of belt-positioning boosters has included development of a surrogate seatbelt retractor. The device is a repeatable, reusable fixture that produces ATD kinematics similar to those seen when a booster is tested with a production seatbelt retractor. The surrogate retractor is being considered for inclusion in a future upgrade of the FMVSS No. 213 standard. Another research project involved identifying possible additional measures for assessing dynamic booster seat performance that include torso angle and knee-minus-head excursion.

FMVSS No. 213 primarily focuses on dynamic testing requirements and labeling specifications. Fit of children within child restraints is generally limited to accommodating 12MO, 3YO, and 6YO ATDs; manufacturers also check child restraint dimensions against key anthropometry measures collected in the 1970s. To provide another tool for assessing fit of different sized children within a particular child restraint, we performed volunteer testing to collect the 3-dimensional shape of toddlers in seated postures. These data are the basis of toddler shape models that can be used virtually to check how different sizes of children would be accommodated by the harnesses and interior dimensions of a child restraint.

Child Restraints in Unconventional Seating

This study used computer models to study how unconventional seating positions and orientations in vehicles with automated driving system (ADS) may affect occupant response metrics for harness-restrained children and vehicle belt-restrained children. We first conducted a literature review to frame a simulation plan, including selections of surrogate ADS-equipped vehicles, potential seating arrangements, impact scenarios, ATD models, and child restraint system (CRS) models that are relevant to the selected ATD occupant models. Due to the lack the impact tests with child ATD and CRS in farside, oblique, and rear impacts, we conducted 16 sled tests with CRS harness-restrained ATDs and vehicle belt-restrained ATDs seated in conventional and unconventional vehicle seat orientations in frontal, farside, oblique, and rear impact conditions, and use the sled tests to validate a set of computational models. A total of 550 MADYMO simulations was then conducted with CRABI 12MO in rear-facing CRS, H33YO ATD in both rear-facing and forward-facing CRS, H36YO in a backless booster and H310YO with and without a booster across a range of conventional and unconventional seating locations and orientations under five impact directions and various CRS installation methods. We did not find major safety concerns in harness-restrained ATDs based on the nature of ATD contacts, although some injury measures are over injury assessment reference values. CRS may rotate laterally in farside and oblique impacts, which could result in higher HIC and chest acceleration due to inertia loading to the CRS, and there is a risk that the larger lateral rotation of the CRS my lead to a contact between CRS and vehicle interior. The major safety concern for vehicle belt-restraint ATDs is that they have the potential to contact the seat next to them or the instrument panel behind them in a farside or oblique impact. Unconventional seating does not necessarily create additional safety concerns beyond what we know with the conventional seating. However, due to the orientation of the unconventional seats, they may involve in higher percentage of oblique and rear-oblique impacts than the conventional seats, which should be considered in future design process. This is the first study using different child ATDs and CRSs to investigate child occupant responses in a wide range of impact directions and seating orientations. Results from the sled tests and simulations provide a better understanding of child occupant responses in those crash conditions, but also identified several limitations of using frontal ATDs in other crash directions.