2. Anthropomorphic Test Device (ATD) families

Anthropomorphic Test Devices are calibrated mechanical surrogates that convert crash-induced motion into measurable physical quantities — accelerations, forces, moments, and deflections — at anatomically meaningful locations. Selecting the correct ATD family is not a matter of preference; it is dictated by the impact direction, the regulatory or consumer-test protocol being targeted, and the injury criteria that must be evaluated. This section maps the major ATD families, explains what each was engineered to measure, and provides a structured selection procedure for side impact applications.

The Two Dominant Lineages: Frontal and Side Impact

ATD families split along the axis of impact direction. Frontal devices — Hybrid III and THOR — are designed for belt-restrained, forward-facing occupants and emphasize chest compression, femur load, and head/neck flexion-extension response. Side impact devices — WorldSID, EuroSID-2, ES-2re, and SID-IIs — are designed for lateral loading, where the dominant injury mechanisms are rib fracture, pelvic ring fracture, and thoracic organ compression against the door trim and armrest.

The Hybrid III family (50th percentile male, 5th percentile female, and the 95th percentile and child variants) remains the workhorse of FMVSS 208 and many frontal regulations. Its key measurable channels are head resultant acceleration, neck axial force and bending moment, chest deflection via a sternal potentiometer, and femur axial force. Hybrid III is a mature, highly repeatable design, but its stiff thoracic spine and simplified shoulder make it a poor surrogate for lateral loading.

THOR (Test Device for Human Occupant Restraint) is the modern frontal successor. It adds a more biofidelic thorax with four-point rib deflection measurement, a flexible lumbar spine, and improved face and clavicle geometry. THOR is specified in FMVSS 208 optional advanced airbag compliance paths and in several consumer protocols. Its richer instrumentation demands more data channels and more careful calibration than Hybrid III.

Side Impact ATD Families

EuroSID-2 and its US variant ES-2re are the established side impact devices for ECE R95 and FMVSS 214 respectively. They measure rib deflection through a three-rib array, abdominal force via a load cell, and pelvic force. The "re" suffix denotes the reduced-arm variant required for the US regulation, which removes the arm to accommodate the side airbag deployment path.

WorldSID is the most biofidelic side impact ATD currently in wide use. Its 50th percentile male version features a fully instrumented thorax with four rib deflection channels per side, a deformable shoulder, and a pelvis with independent iliac and pubic load measurement. WorldSID is specified in UN R135 (pole side impact) and in Euro NCAP and other consumer programs. Its complexity means higher unit cost and stricter calibration tolerances, but it provides the most detailed injury-risk picture available.

SID-IIs is the small female side impact device, used to assess occupant protection for smaller stature occupants. It is required in FMVSS 214 and is increasingly used in consumer testing to capture the elevated injury risk that small occupants face in lateral collisions.

Selection Criteria for Side Impact Testing

Choosing a side impact ATD is a protocol-driven decision. The following decision logic applies:

• Regulatory target: If the test must satisfy FMVSS 214, use ES-2re (or SID-IIs for the small female requirement). If it must satisfy UN R95 or R135, use EuroSID-2 or WorldSID as specified.
• Consumer program: Euro NCAP side impact and pole tests specify WorldSID 50th. Check the current protocol year, as ATD specifications are revised periodically.
• Injury criteria to be evaluated: If rib fracture risk (RibDef) and abdominal injury are the primary concern, WorldSID provides the most channels. If pelvic injury is the focus, both WorldSID and ES-2re provide pelvic load cells, but WorldSID separates iliac and pubic loads.
• Occupant size: Match the ATD percentile to the occupant population under study. A 5th percentile female test requires SID-IIs; a 50th percentile male test requires WorldSID or ES-2re.
• Vehicle geometry: Armrest height, door trim stiffness, and seat-mounted airbag position influence which ATD can be seated without interference. The ES-2re reduced-arm variant exists specifically to avoid arm-airbag interaction.

Instrumentation and Channel Mapping

Each ATD family exposes a different set of measurement channels. The table below summarizes the primary channels for the side impact devices most relevant to this course.

Note that WorldSID's four-rib thorax provides deflection data at multiple heights, which allows the analyst to distinguish upper-rib from lower-rib loading — a distinction that matters when evaluating door trim and armrest geometry. ES-2re and EuroSID-2 provide three ribs, which is sufficient for regulatory pass/fail but less informative for design optimization.

Calibration and Certification Implications

ATD family selection directly determines the calibration burden. Hybrid III and ES-2re have well-established, relatively forgiving calibration corridors. WorldSID requires tighter tolerances on rib deflection linearity and pelvic load cell zeroing, and its shoulder assembly must be checked for free rotation before every test. THOR adds a lumbar spine compliance check and a face load sensor calibration that Hybrid III does not require.

In practice, a test laboratory running both frontal and side impact programs will maintain separate calibration fixtures for each family. The certification engineer must verify that the ATD serial number, calibration date, and channel list match the test request before the dummy is seated. A mismatch between the requested ATD and the calibrated unit is one of the most common causes of invalid test data.

Selection Workflow

The following workflow summarizes the decision path from protocol identification to ATD confirmation. It is intended to be used as a checklist during test planning.

1. Identify the governing protocol and revision year (e.g., FMVSS 214, UN R95, Euro NCAP 2024).
2. Extract the specified ATD family, percentile, and variant from the protocol text.
3. Confirm the required instrumentation channels and injury criteria.
4. Verify that the laboratory has a calibrated unit of that exact family and variant available for the test window.
5. Check seating procedure and vehicle geometry compatibility (armrest, door trim, airbag path).
6. Lock the ATD selection and record it in the test request and build documentation.

The map above is not a substitute for the protocol text. It is a planning aid: it forces the engineer to resolve the protocol, the impact direction, and the occupant percentile before committing to an ATD. In practice, the most expensive mistakes in side impact testing come from selecting the right family but the wrong variant — for example, ordering a WorldSID 50th when the protocol requires the 5th percentile female, or using an ES-2re when the test is governed by UN R95 and requires EuroSID-2. The verification bar at the bottom of the diagram is the last line of defense: confirm the ATD family, variant, calibration certificate, channel list, and seating procedure against the test request before the dummy is instrumented and seated.