A car advertised as top rated has passed a specific set of staged collisions, each designed to reproduce one crash type. The rating describes performance in those scenarios, not safety in general.
Tests reproduce defined collision types
Frontal tests drive a vehicle into a fixed barrier at a set speed, either across the full width of the front or against a narrower overlap that engages only part of the structure.
Side tests strike a stationary vehicle with a moving barrier shaped and weighted to represent another vehicle striking it. Roof strength tests press a plate against the roof pillar until it deforms.
Each test isolates one loading path through the structure, which is why a vehicle can perform very well in one and less well in another.
Instrumented dummies supply the injury measures
Crash test dummies carry sensors recording acceleration, force and displacement at the head, neck, chest, pelvis and legs during the fraction of a second the collision lasts.
Those readings are compared against injury criteria derived from biomechanical research, producing an estimate of the likelihood of injury to each body region.
Dummy families include different sizes, and results can differ across them, which is one reason testing programs have expanded the range of occupants they represent.
Structure and restraints are scored separately
Beyond dummy readings, evaluators measure how much the occupant compartment intruded, since a collapsed footwell or door opening indicates the structure did not manage the load.
Restraint performance is judged by whether belts and airbags kept the dummy in position, since an airbag that deploys correctly but is bypassed by dummy motion offers less protection.
A vehicle can therefore lose points for occupant kinematics even when measured forces stay low, because the test is assessing the whole protection system.
Crash avoidance now sits alongside crashworthiness
Modern rating programs also evaluate systems intended to prevent a collision, including automatic emergency braking assessed by driving toward a target at defined speeds.
Headlight performance is measured too, since visibility distance affects the driver's ability to react at all. These evaluations are separate from the collision tests.
Top awards increasingly require good results in both categories, which is why a structurally strong vehicle can miss an award on lighting or braking alone.
Ratings compare within a class, not across all vehicles
Tests run at fixed speeds against fixed barriers, so results reflect how a vehicle protects its own occupants under those conditions rather than how it fares against a much heavier vehicle.
Physics still applies in real collisions between mismatched vehicles, and rating programs state this limitation directly rather than implying equivalence across size classes.
Test protocols also change over time, which means a rating earned under an older protocol is not directly comparable to one earned under a newer, more demanding version.