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.
Disabilities affect a wide range of the U.S. population. According to the U.S. Census Bureau, based on data from the most recent census in 2010, a total of 56.7 million people - 19 percent of the U.S. population - had a disability at the time of the census.