I have some new trucks. the left pedal have an electrical switch, then there is not a brake pump asociated to this pedal.
when you press it, the trucks does not have traction, and slowly will stop. But if you are in a tilt, the truck will go down still if you are pressing the left pedal.

If you need to stay quiet the truck completely, you have to press the brake button that is in the levers zone (red button)

I hope was useful,