The Mercedes-Benz CLA shares its active safety technology with the A-Class, assessed by Euro NCAP in 2018. Hardware is the same and the two cars' systems perform equivalently. Accordingly, active safety results are based on those of the A-Class.  As the front seats and head restraints are also identical, the results of the A-Class have also been used for rear-end whiplash protection.  All full-scale crash tests have been repeated.

The passenger compartment of the CLA remained stable in the frontal offset test. Dummy readings indicated good protection of the knees and femurs of both the driver and passenger. Mercedes-Benz showed that a similar level of protection would be provided to occupants of different sizes and to those sitting in different positions. In the full-width rigid barrier test, protection of all critical body areas was good or adequate for both the driver and the rear passenger. In the side barrier impact, dummy readings showed good protection of all body areas. However, the rear door on the impacted side of the car opened during the test and the score was penalised for the risk of occupant ejection.  In the more severe side pole test, protection of the chest was adequate and that of other critical body regions was good. 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 autonomous emergency braking (AEB) system performed well in tests of its functionality at the low speeds, typical of city driving, at which many whiplash injuries are caused, with collisions avoided or mitigated in all test scenarios.

In the frontal offset test, dummy readings showed good or adequate protection of all critical body areas for both the 6 and 10 year children. In the side barrier test, protection was good for all critical parts of the body, except for the head of the 10 year child, which was rated as adequate, based on readings of head acceleration. The CLA has a system that automatically recognises when a rearward-facing child restraint has been put in the front passenger seat and deactivates the airbag for that seating position. Mercedes-Benz showed that the system worked robustly and it was rewarded. All of the restraint types for which the CLA is designed could be properly installed and accommodated.

The CLA has an active, deployable bonnet. Sensors in the bumper detect when a pedestrian has been struck and actuators lift the bonnet surface to provide greater clearance to the stiff structures in the engine compartment. Mercedes-Benz showed that the system worked robustly for different pedestrian statures and across a wide range of speeds, so tests were performed with the bonnet in the raised position. Protection was good at almost all test locations on the bonnet. Protection was also good for the leg and pelvis areas of a struck pedestrian. The AEB system performed well in tests both of its pedestrian detection and its response to cyclists, with collisions avoided in nearly all test scenarios.

The AEB system performed well in tests of its functionality at highway speeds. The lane assistance system performed marginally, with adequate performance for lane keeping assistance and emergency lane keeping but lacking a blind-spot monitoring system. The speed assistance system, comprising a camera-based speed limit detection system and driver-set speed limiter, was rated as good. The car has a seatbelt reminder system as standard for front and rear seats.