The gate is probably manually opened and manually closed, and he probably does this everyday or often enough to get tired of the process and feel a need to streamline it for increased efficiency.
Instead of the standard process:
stop, park, get out, raise gate, get in, drive, stop, park, get out, lower gate, get in, drive.
He wanted something with fewer steps, possibly just to see if he could do it.
stop, park, get out, drive, raise gate, (car slips through on idle), lower gate, jump in car, drive.
But his car idled too quickly, causing the car to move too quickly before he could raise the gate.