If the company doesn’t have enough drivers/vehicles and that problem isn’t being resolved and they are simply relying on drivers to pick up management’s problem. Then that’s basically a plaster over a gunshot wound in effect. It will only last so long before the drivers are burnt out, stressed and have more and more accidents. Which will probably then be let go due to that fact and any reference wont be great due to the accidents…
As hard as it might be to hear. Your role should be to drive the vehicle in a safe manner and carry out the work you can in a reasonable way. Your role isn’t to help the company when it, itself wont invest/spend more for additional drivers.
If it is affecting your out-of-work life, then I would begin to consider how you can improve things.
If companies are paying for a service they don’t receive, they will change companies so they do receive what they pay for - That isn’t your problem as a driver though.