4. Euro NCAP adult occupant protection
Side impact is where the adult occupant protection score is most easily lost. Unlike the frontal offset test, where a large crumple zone absorbs energy over hundreds of milliseconds, a side impact delivers energy through a door panel that sits only 200–300 mm from the occupant's hip. Euro NCAP therefore evaluates side protection with two complementary configurations: a moving deformable barrier (MDB) side impact that represents a car being struck in the driver's door, and a far-side impact that represents the occupant on the struck-opposite side being thrown across the cabin. Both feed the same Adult Occupant Protection (AOP) score, but they test different physics and use different dummies, barriers, and point scales.
Barrier specifications and test geometry
The MDB test follows the UN R135 / Euro NCAP side impact protocol. The barrier is a deformable aluminium honeycomb face mounted on a rigid trolley. Its key parameters are fixed and must be verified before every test:
- Barrier mass: 950 kg total (trolley plus deformable face), representing a mid-size striking vehicle.
- Impact speed: 60 km/h, with the barrier travelling perpendicular to the struck vehicle's longitudinal axis.
- Deformable face: 1500 mm wide × 500 mm high, with a honeycomb crush characteristic tuned to approximate a car front end. The face centre is aligned with the struck vehicle's R-point height.
- Ground clearance: the barrier's lower edge sits 300 mm above the ground plane, so the load path enters the door structure below the beltline.
- Struck vehicle: stationary, in neutral, with the driver's seat set to the manufacturer's design position and the dummy installed per the seating procedure.
The far-side test uses the same 950 kg MDB at 60 km/h, but the barrier strikes the passenger side while the instrumented dummy sits in the driver seat. This is the critical distinction: the struck side has no dummy, and the driver is a free body accelerated laterally by the cabin's yaw and lateral displacement. The far-side dummy therefore experiences a different loading regime — the seat belt and side airbag on the non-struck side must restrain the occupant, and the risk is head excursion across the centreline and interaction with the far door or the other occupant.
Dummy instrumentation
Euro NCAP side impact uses the WorldSID 50th percentile male dummy, which replaced the older ES-2re. WorldSID is a far more heavily instrumented anthropomorphic test device, and the additional channels are exactly what the point allocation rewards. The channels that matter for scoring are:
| Body region | Channel (representative) | What it measures |
|---|---|---|
| Head | Head CG triaxial acceleration, head rotational velocity | Linear and angular loading; used for HIC and brain injury criteria |
| Neck | Upper neck forces and moments (Fx, Fy, Fz, Mx, My, Mz) | Neck bending and shear during lateral head excursion |
| Chest | Rib deflection (4 ribs, left and right), chest acceleration | Rib fracture risk; the primary chest injury metric |
| Abdomen | Abdominal pressure / deflection | Soft-tissue injury from door intrusion |
| Pelvis | Pubic symphysis force, iliac wing force | Pelvic fracture risk |
| Femur | Femoral forces (left and right) | Femur loading from door contact |
Each channel is sampled at 10 kHz or higher and filtered per the protocol (CFC 600 for accelerations, CFC 180 for deflections). The dummy must be calibrated and its certification date valid; an out-of-calibration WorldSID invalidates the test regardless of the measured values.
Point allocation
Euro NCAP awards AOP points per body region, and the side impact test contributes to the head, chest, abdomen, pelvis, and femur sub-scores. The scoring logic is threshold-based: each channel has a lower performance limit (full points) and an upper performance limit (zero points), with linear interpolation between them. A representative chest rib deflection of 28 mm might earn full marks, 42 mm zero, and 35 mm roughly half. The exact limits are set in the current Euro NCAP protocol and are revised with each rating year, so always score against the protocol version in force for the test date.
Two structural rules matter in practice. First, the worst channel governs the region: if any single rib deflection exceeds the upper limit, the chest region scores zero even if the other ribs are well within limits. Second, far-side performance is scored separately and can cap the overall AOP result — a vehicle that performs well in the MDB test but allows excessive far-side head excursion will lose points that cannot be recovered elsewhere. The far-side assessment also includes a submarining and belt-slip check, because the occupant loading path in far-side impact is dominated by the belt geometry rather than door intrusion.
Reading a test result
After the test, the measured channels are filtered and compared against the protocol limits. A practical workflow for interpreting a side impact result is:
- Check test validity first. Confirm barrier speed within tolerance (±0.5 km/h), barrier alignment, dummy calibration, and that the seat and belt were in the design position. An invalid test is not scored.
- Inspect the intrusion profile. Door intrusion at the occupant's hip and chest should be compared with the pre-test geometry. Excessive intrusion explains high rib deflections and is a structural, not a restraint, problem.
- Score each region from the worst channel. For the chest, take the maximum of the four rib deflections; for the head, compute HIC and check the rotational criteria; for the pelvis, take the peak pubic symphysis force.
- Review the far-side result separately. Check head excursion across the centreline, belt slip, and submarining. A far-side head excursion beyond the protocol limit caps the AOP score even if the MDB test was clean.
The key takeaway for scoring is that side impact is a region-by-region, worst-channel-governed assessment, and far-side impact is a separate gate that can cap the result. Barrier parameters (950 kg, 60 km/h, honeycomb face) and dummy instrumentation (WorldSID with rib deflection, pelvic force, and head rotational channels) are fixed by protocol, so the engineering effort belongs in the door structure, the side airbag, and the belt geometry — the three things that determine whether the measured channels land below the lower performance limits.