Employers generally need to compensate employees' medical bills who have sustained injuries while on the physical premises. However, if an employee suffers an injury while driving to or from work, then he or she would be unable to collect workers' compensation. Since you are on the commute, you are not technically at work yet, so the employer is not liable for any injuries sustained.
Due to this rule, many employers also mistakenly believe they are not liable for any injuries if the worker has to go out and run an errand. As long as the employee is on the clock and receiving payment for the task, then he or she would absolutely qualify for workers' comp. However, there are always some gray areas even in terms of running a special errand.
Your boss may send you out to meet with a client. Before you head back to the office, you do not see the harm in heading over to the bank to take care of a few things. If you get into a car accident while on your way to the bank, then the insurance adjuster would see you were not on a path back to the office when you got into the crash. Since you also conducted business-related tasks during the venture, your injuries may still qualify for compensation. It comes down to the exact circumstances surrounding the incident.
Some employees are on-call, which means they only go in to work when the employer has a direct need from them. Similarly to everyone else, this on-call employee may suffer an injury in a car crash while commuting to the jobsite. Normally, this would not apply for workers' comp. However, there are cases where employees would qualify for workers' comp in this instance, such as if the boss pays them as soon as they accept the assignment.