4. ES-2 side impact dummy

The ES-2 (European Side Impact Dummy, second generation) is the workhorse anthropomorphic test device (ATD) for European side impact regulation and remains widely used in consumer and development testing. Understanding its lineage, instrumentation, and the specific ways it diverges from WorldSID is essential for anyone interpreting side impact injury metrics, because the two dummies do not measure the same things in the same way — and their outputs are not interchangeable.

From EuroSID-1 to ES-2: What Changed and Why

The original EuroSID-1 (EEVC side impact dummy) was developed in the late 1980s to support ECE Regulation 95. It used a rigid, segmented ribcage with three rib modules on the struck side, a deformable arm, and a simple pelvis. While it captured the broad kinematics of a side impact, its biofidelity was limited: the ribcage was stiff, the shoulder was not well represented, and the abdomen lacked a dedicated deflection measurement. These shortcomings became apparent as real-world crash data showed that abdominal and pelvic injuries were under-predicted.

ES-2, introduced in the late 1990s and mandated under ECE R95 (as amended) and later Euro NCAP protocols, addressed these gaps with several targeted changes:

• Revised ribcage geometry and compliance. The three struck-side ribs were re-shaped and tuned to better match human chest force–deflection characteristics, reducing the over-stiff response of EuroSID-1.
• Added abdominal rib and abdomen force/deflection sensing. ES-2 introduced a dedicated abdominal rib element and an abdomen insert, allowing separate measurement of abdominal loading — a region EuroSID-1 effectively ignored.
• Improved shoulder and arm. The shoulder block and arm were redesigned to better represent the load path from the door into the thorax, and to reduce unrealistic arm stiffening during impact.
• Pelvis and iliac wing refinement. The pelvis was reshaped to improve hip loading representation and to provide a more realistic pubic symphysis load path.

The result is a dummy that is still fundamentally a deflection-based device: its primary injury criteria are derived from rib deflections measured by potentiometers, not from accelerations alone. This is the single most important fact for interpretation — ES-2 tells you how much the chest and abdomen compressed, which is a direct mechanical proxy for organ loading.

ES-2 Sensor Configuration

A standard ES-2 build for regulatory side impact carries the following instrumentation. Note that channel names and locations matter: a "chest deflection" from ES-2 is a specific rib potentiometer output, not a generic chest metric.

Two practical points dominate ES-2 data quality. First, the rib potentiometers are calibrated against a known deflection and are sensitive to pre-load and seating; a dummy that is not properly seated against the door trim will show artificially low deflections because the rib has already been displaced before impact. Second, the abdomen force sensor and pubic load cell are easily damaged by handling and must be zeroed and range-checked before every test. A common field failure is a drifting abdomen channel that reads a non-zero baseline — this corrupts APF and is often mistaken for a real abdominal load.

ES-2 versus WorldSID: A Structural Comparison

WorldSID was developed later (mid-2000s onward) as a globally harmonized side impact dummy, and it differs from ES-2 in ways that directly affect how you interpret injury numbers. The most consequential differences are the sensing principle and the body region coverage.

ES-2 measures chest and abdominal deflection via potentiometers on discrete ribs. WorldSID measures rib deflection as well, but with a denser array of ribs (more rib elements per side) and, critically, it is designed around a more biofidelic, multi-rib thorax with improved shoulder and pelvis geometry. WorldSID also provides a more complete set of load cells (including a dedicated shoulder load cell and more detailed pelvic instrumentation) and is built to a single global specification rather than regional variants.

The practical consequence: ES-2 and WorldSID injury criteria are not directly comparable. An ES-2 RDC of, say, 40 mm and a WorldSID chest deflection of 40 mm are measured on different rib geometries with different compliance, so the same number does not imply the same injury risk. When a program transitions from ES-2 to WorldSID, the injury assessment reference values (IARVs) and the pass/fail thresholds must be re-derived; you cannot carry an ES-2 limit across.

Interpreting ES-2 Outputs in Practice

Because ES-2 is deflection-based, the interpretation workflow centers on the rib potentiometer traces. A typical post-test review proceeds as follows. First, confirm the time-zero alignment across all channels using the trigger signal; a misaligned rib channel will produce a deflection curve that appears to lead or lag the acceleration channels, which is a data-processing error, not a physical result. Second, inspect each rib deflection trace for the peak value and the time of peak. The peak deflection is the input to the RDC calculation, which normalizes deflection against a reference and applies a scaling; the exact formulation depends on the regulation version in force, so always cite the protocol revision alongside the number.

Third, cross-check the abdomen force and pubic load against the deflection traces. A high abdominal force with a modest abdominal deflection can indicate a load path through the arm or door that bypassed the rib — a pattern worth flagging in the report even if the deflection criterion passes. Fourth, verify that the pelvis and femur channels are physically plausible; a pubic force that is orders of magnitude above the expected range usually means a sensor range or calibration error rather than a genuine injury signal.

Where ES-2 Still Fits

Despite WorldSID's broader adoption, ES-2 remains relevant for legacy regulation compliance, for programs with existing ES-2 databases that need continuity, and for development work where the deflection-based chest and abdomen signals are well understood by the engineering team. The key discipline is to treat ES-2 as a specific instrument with a specific measurement principle — not as a generic "side impact dummy" whose numbers can be swapped with any other. Knowing its evolution from EuroSID-1 explains why its rib and abdomen channels exist at all; knowing its sensor layout explains what each channel physically measures; and knowing its divergence from WorldSID explains why the numbers must be interpreted within their own protocol and never carried across dummy types.