A few years ago, toll takers began getting shocks from drivers because new tires on some cars allowed the cars to build a static charge. One solution was to drag a grounding strip.
That would ground the car. Depending on the upholstery material and his shoe soles, the driver may get a shock when he gets out, either opening or closing the door. A static charge can build between two objects when they are insulated from each other, even for a moment.
The driver can probably discharge himself painlessly by touching the glass.