3. Euro NCAP adult occupant protection

Adult Occupant Protection (AOP) is the largest single pillar in the Euro NCAP overall rating, and the two frontal crash configurations — the Offset Deformable Barrier (ODB) test and the Mobile Progressive Deformable Barrier (MPDB) test — carry the heaviest weighting within it. Both are full-scale vehicle-to-barrier impacts, but they answer different engineering questions: ODB asks how well a car protects its own occupants when it strikes a deformable object with only part of its front end, while MPDB asks how the car behaves when it hits a moving, deformable counterpart — and, critically, how aggressively it treats the other vehicle. This chapter explains the test setups, the injury criteria measured on the crash dummies, and how raw sensor data becomes a scored result.

Test setup: what is actually impacted, and how

In the ODB test, the vehicle is driven longitudinally into a fixed, deformable barrier at 64 km/h. The barrier consists of a rigid block faced with a honeycomb aluminium element, and it overlaps only 40% of the vehicle width on the driver's side. The 40% overlap deliberately loads one longitudinal member and one wheel/suspension path far more than the other, producing asymmetric intrusion into the occupant compartment — a far more demanding structural case than a full-width rigid wall. The vehicle carries two Hybrid III 50th-percentile male dummies, one in the driver seat and one in the front passenger seat, restrained by the production seat belts and airbags.

The MPDB test replaces the fixed barrier with a trolley-mounted deformable barrier that is itself moving. The trolley, carrying a honeycomb-faced barrier, travels toward the test vehicle; the combined closing speed is 50 km/h per vehicle, giving a 100 km/h closing speed, with 50% overlap. Because the barrier moves, the impact energy and the post-impact kinematics differ fundamentally from ODB: the barrier deforms, the trolley decelerates, and the test vehicle is pushed and rotated rather than stopped against an immovable object. The MPDB barrier face is instrumented and its deformation is measured, which is what enables the compatibility assessment described below.

Injury criteria measured on the dummies

Euro NCAP does not score "damage"; it scores injury risk derived from dummy instrumentation. Each body region has its own criterion and its own reference limits. The most important ones for frontal impact are:

• Head: Head Injury Criterion (HIC15), computed from the resultant head acceleration over the most severe 15 ms window, plus a separate check on head contact with the steering wheel or dashboard (head excursion and contact evidence).
• Neck: neck tension, compression, shear force and bending moment, assessed against limit values in each direction.
• Chest: chest deflection (compression) and the Viscous Criterion (VC), which captures the rate-dependent soft-tissue injury risk that pure deflection misses.
• Abdomen and pelvis: force and deflection limits, particularly relevant where the belt path loads the lower torso.
• Femur and knee: axial femur force and knee displacement, which flag lower-limb loading from the knee bolster and footwell intrusion.

Each criterion is normalised against a reference limit. A measured value at or below the "low" limit earns full points for that body region; a value at or above the "high" limit earns zero; values in between are interpolated. This is why a modest chest deflection increase of a few millimetres can move a score by a meaningful fraction of a point — the scoring is continuous, not pass/fail.

From sensor traces to a score

The scoring pipeline is worth understanding because it explains why engineers chase small changes. For each dummy and each body region, the measured criterion is converted to a normalised injury value using the low/high limits, then mapped to a point score. The region scores are combined into a dummy score, and the driver and passenger scores are combined into the frontal impact score. In MPDB, an additional compatibility assessment is layered on top: the barrier's own deformation is analysed to estimate the stiffness the test vehicle presented to the partner, and a penalty is applied if the vehicle is judged overly aggressive (for example, a stiff, narrow front structure that concentrates force into the barrier).

Consider a worked example with illustrative (not measured) numbers. Suppose the driver dummy records HIC15 = 480, chest deflection = 32 mm, and VC = 0.12 m/s. If the HIC15 low/high limits are 500/700, the head is at full points. If chest deflection limits are 22/50 mm, 32 mm sits partway up the scale and yields a partial score. The engineer reads the trace, sees the chest deflection peak coincides with belt spool-out and a late airbag cushion, and targets restraint tuning rather than structure. That is the practical loop: criterion → normalised value → score → physical cause.

Practical reading of results and common failure modes

When a frontal test underperforms, the symptom usually points to a specific subsystem. A high HIC15 with visible head-to-steering-wheel contact suggests insufficient restraint or a late-deploying airbag; a chest deflection peak that coincides with belt force spikes points to belt geometry or load-limiter calibration; asymmetric femur loading in ODB often traces to footwell intrusion on the impacted side, which is a structure problem rather than a restraint problem. In MPDB, a poor compatibility result with acceptable occupant scores is the classic signature of a front end that is too stiff and too concentrated — the car protects its own occupants but pushes excessive force into the partner barrier.

Because the scoring is continuous and region-weighted, the productive engineering workflow is to plot each criterion against its low/high band, identify which region is leaving points on the table, and then trace that region back to the physical mechanism in the high-speed video and the sensor traces. The score is the summary; the traces and the barrier deformation are the diagnosis.

The key takeaway for rating calculation is that frontal AOP is not a single number pulled from a single crash. It is a weighted aggregation of normalised injury criteria across two dummies and two test configurations, with MPDB adding a compatibility dimension that rewards front structures designed to be both protective and courteous to the other vehicle.