Who's responsible in this car accident?

I'd a car accident. The driver of the other vehicle isn't the owner of the car. He's the worker at the commercial property, the accident took place at the commercial property. Who is responsible in the case? The insurance of the commercial property or car insurance of the other vehicle, or both in this case?
It's the other driver.
I wonder who is responsible on his side

If the driver was in the course and scope of his employment and had permission to use the vehicle, the commercial property owner's insurance company would provide coverage to the driver. He would be considered an "insured" by definition under the commercial auto policy. The driver's personal auto would likely deny coverage if he was working at the time of the accident, but that would be subject to interpretation of his personal auto policy.

Call the commercial property's insurer and file a claim. They will complete an investigation and let you know if they accept liability.