When a person is hurt by someone who was driving for a living, the first fight is rarely about the driving. It is about one word: scope.
The old rule is that an employer answers for the wrongs of an employee committed within the scope of employment. The lawyers call it respondeat superior, let the master answer. The reason is plain. The company put the vehicle on the road, set the schedule, and took the profit, so the company carries the risk that rides with it.
The escape hatch is an older pair of words: frolic and detour. If the worker had stepped entirely outside the job, off on a personal errand of his own, the employer may not answer for what happened during it. A small detour inside the work is one thing. A true frolic, the worker on his own business, is another. Companies reach for that line hard, because if the driver was off the clock and on his own, the company's deep pocket steps back and only the driver's thin coverage is left.
That is why scope is worth more than fault in the opening rounds. A working driver's personal policy is often small. The company behind him is not. Establish that the driver was doing the company's work, in the company's interest, and the company is in the case.
And scope is not decided by what the company says after the fact. It is proven from the record the work itself creates: the dispatch, the route, the logs, the telematics and the black box, the messages telling the driver where to be and when. That trail shows whether the trip served the employer, and it is hard to argue a personal frolic against a load being hauled on the company's own schedule.
Fault tells you the driver was careless. Scope tells you who pays for it. Find the word first.
On an employer's responsibility for an employee acting within the scope of the work, see the doctrine of respondeat superior and its frolic-and-detour limit, long settled in the common law of agency. This is general information, not legal advice.