The passenger compartment of the Mazda 3 remained stable in the frontal offset test. Dummy readings showed good protection for all critical body regions of the passenger. Good protection was provided to the knees and femurs of both the driver and passenger. Mazda showed that a similar level of protection would be provided to occupants of different sizes and those sitting in different positions. In the full-width, rigid barrier test, maximum points were scored for the front driver and rear passenger occupants, with good protection of all critical parts of the body. Similarly, in the side barrier test and the more severe side pole impact, all parts of the body were well protected and the car scored full points. Tests on the front seats and head restraints demonstrated good protection against whiplash injuries in the event of a rear-end collision. A geometric assessment of the rear seats also indicated good whiplash protection. The standard-fit autonomous emergency braking (AEB) system, known as 'Smart Brake Support', performed well in tests of its functionality at the low speeds, typical of city driving, at which many whiplash injuries occur. Collisions were avoided in all test scenarios.

In the frontal offset test, good protection was provided to both the 6 and 10 year infants. Similarly, in the side barrier impact, all critical parts of the body were well protected for both dummies and the Mazda 3 scored maximum points for its performance for child protection in the dynamic tests. The front passenger airbag can be disabled to allow a rearward-facing child restraint to be used in that seating position. Clear information is provided to the driver regarding the status of the airbag and the system was rewarded. All of the child restraint types for which the Mazda 3 is designed could be properly installed and accommodated.

The protection provided by the bonnet to the head of a struck pedestrian was predominantly good, and at least adequate over almost all of the surface. Protection of pedestrian's legs and of the pelvis area was good in all test areas and the Mazda 3 scored maximum points. The AEB system can detect vulnerable road users such as pedestrians and cyclists. In tests of these functionalities, the system demonstrated good performance for pedestrians and adequate performance in the more challenging cyclist scenarios.

The 2019 Mazda 3 has a seatbelt reminder for the front and rear seats as standard. The AEB system performed well in tests of its functionality at highway speeds. The speed assistance system uses a camera and digital mapping to identify the local speed limit and offers the driver the opportunity to set the limiter appropriately. The lane support system assists in preventing the vehicle from drifting out of lane but does not intervene in more critical scenarios, as do the systems on some cars.