The passenger compartment of the GLB 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 regions was good or adequate with the exception of the neck of the driver, for which dummy readings of tensile forces indicated a marginal level of protection. In the side barrier test, protection of all critical body areas was good and the GLB scored maximum points. In the more severe side pole test, dummy readings of rib compression indicated marginal protection for the chest, with other critical parts of the body being well protected. 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 performed well in tests of its functionality at the low speeds, typical of city driving at which many whiplash injuries occur.

In the frontal offset test, readings of tensile forces indicated weak protection of the neck of the 10-year dummy. Otherwise, protection of critical body areas was good for both dummies. In the side barrier test, protection of all critical body areas was good or adequate. The front passenger airbag is automatically disabled when a rearward-facing child restraint is put in that seating position. Tests showed that the system worked robustly and the system was rewarded. All of the child restraint types for which the GLB is designed could be properly installed and accommodated.

The GLB 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 or adequate at almost all test locations on the bonnet. The bumper provided good protection to pedestrians' legs at all test positions. However, the protection provided to the pelvis area was poor and the GLB scored no points in this part of the assessment. 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. A lane assistance system helps to prevent inadvertent drifting out lane by warning the driver and gently applying some corrective steering. The system also intervenes more aggressively in some more critical situations. A camera is used to determine the local speed limit. This information is presented to the driver who can choose to let the limiter adapt the speed accordingly. The car has a seatbelt reminder system as standard for front and rear seats.