Sliding are the most secure automatic gate systems around. Due to the nature of their operation and positioning, when closed they are almost impossible to open. They are held in place by the tracking system, drive motor, and other features of the installation, such that they cannot be wedged sideways except by very unusual and extreme force.
Sliding Gates would normally run back and forth on grooved or circular wheels along a level horizontal beam fitted with a channel. The motor will drive the gate back and forth using a rack and pinion mechanism on the gate, powered by a cog at low level on the gate motor. This configuration however does require that the ground is relatively level and that a steel beam can be sunk into the ground the full length of the gate in both the open and closed positions.
An alternative method of operation is the Cantilever System. Here there is no sunken steel beam the full length of the gate plus itself again. Instead the entire gate is suspended on a relatively short cantilever system involving wheels set in a channel (rather like the wheels of a train carriage). The gate motor principle is the same (i.e. toothed rack and pinion), with the motor being located in roughly the same position as with a standard sliding gate system.
Due to the design and direction of automatic sliding gates the "hydraulic vs. electromechanical" argument does not enter into the equation. Sliding gates by their very nature cannot be hydraulic in operation. They require to be able to engage or disengage when under, at or over recommended thrust levels, in order that the motor does not fail. This operates rather like a clutch in car, which engages to drive and disengages to idle.