Unfortunately, we learned what happened at the May 1st kindergarten in Pile, province of L’Aquila. But, technically, is an explanation possible? Let’s try to shed some light on what the parking protocol usually is.
What does the manual say?
Parking brake activated and low gear engaged, if you are downhill also wheels towards the pavement. To leave the car parked on a descent, with the nose down, each driving course indicates these three maneuvers as essential to prevent the vehicle – once abandoned – from starting to move without control. The combination of the three maneuvers is amply sufficient to avert the danger, given that even one of them, in most cases, is able to prevent the car from moving by picking up speed.
In particular, correct activation of the handbrake and engagement of first gear (manual gearbox), or the “P” position of Park (automatic gearbox) originally prevent the car from moving. Furthermore, among the parking brakes, the most recent electronically controlled electric version, the one in which the classic lever is replaced by a button, is far safer.
To deactivate the electric parking brake, the driver must perform a precise maneuver. He is asked to press the brake pedal fully, or – if the automatic deactivation at departure function is active – start the vehicle first, again having to fully press the brake pedal, which must be activated together with the brake pedal. clutch if the gearbox is manual, then engage a gear and accelerate.
In the case of a manual handbrake with lever (or pedal) activation, any unwanted movement of the car can occur by partial activation, therefore not sufficient for the mechanical tie rods to block the brakes. In this case the lever is up, but the car can move. This is not exactly a rare case with old hand brakes and for careless drivers.
With the low gear engaged, the movement of the old cars is possible by turning the ignition key. This action, even downhill, however, simply produces a jolt, if not accompanied by a rather complex maneuver of skilful actuation of the clutch to get the engine started with appropriate accelerator modulation. In cars with automatic transmission, the “P” position does not allow the engine to start.
Unwanted movement of a car with the electric parking brake on, as well as from a maneuver performed by those on board, can be caused by a malfunction. In the case of electric-electronic mechanisms, the fault may concern the button and the control unit, or the electric motors dedicated to closing the brakes. In both cases, the manufacturers provide warning lights which warn the driver of possible problems.
If the electronic mechanism connected to the button does not work, the handbrake is not activated, so in fact the car is not braked. This is a remote hypothesis, in the eventuality signaled by special warning lights on the dashboard but possible and very dangerous, because the correct maneuver by the driver does not correspond to the expected effect. The car is therefore free to move. If the problem is related to the electric motors that are not working or have been incorrectly calibrated (they therefore come into action, but do not close the brake sufficiently), again the warning lights warn the driver and the car can only be partially braked or even be free. to move, in a similar way with respect to the eventuality of the manual brake lever being partially activated. The hypothesis is very remote, given the existing on-board controls, but possible.
The further possibility for the unwanted and unexpected movement of a car with an apparently engaged electric handbrake relates to a poorly performed maintenance operation or a tampering with the system. A potential problem with electrical systems is opposite to the free movement of the vehicle and relates to the inability to unlock the wheels. This can happen due to a low battery, or a breakdown. For this reason, the workshop manual always provides for a maneuver that allows you to manually release the handbrake. However, this is a professional intervention, which involves the disassembly of components and access to release screws. It cannot be performed from inside the car, nor by a simple driver but requires a professional with adequate knowledge and tools.
The handbrake, so foul, is not in fact functional and the cars have specific mechanisms that prevent it from running in these conditions. For this reason, in addition to unlocking, to circulate the car it would also require tampering, or a further malfunction of the safety systems. Here we are in the field of the almost impossible, but it is still a hypothesis to be analyzed