If the accident only involved one car—if the driver ran off the road or struck a pothole, for example—then the driver of the car will be the one liable for damages. The driver of the car you are riding in should be able to pay for your injuries as well as his own through his policy, but splitting the limit of the coverage between you can leave you both underpaid.
The more people who are injured in a crash, the less each one will be awarded for his injuries. For example, if three passengers sustain injuries and are awarded damages through the negligent driver’s insurance, the passengers will have to split the total amount of the coverage under the driver’s insurance. If the insurance payout is not enough to cover their injuries, the passengers may have to file an injury suit.