Don't assume everyone has car insurance

In most cases, after an auto accident, parties exchange information with one another at the scene of the accident. In some cases, this is done between the parties without any police involvement, especially if there has been no injury and the property damage is minor.  If someone was injured, the police may come to the scene to investigate.  In that case, police officers often separate the parties from one another so they can get independent accounts of what happened.  

The police officers usually will collect insurance information from each party.  In many cases, that insurance information won't be shared with the parties at the scene.  Instead, the officers will recommend you obtain the police report which will have all the information on it.  The problem is that some police reports takes weeks, sometimes months, to be prepared and made available to the parties.  This can be problematic when you are trying to get your car fixed or make a claim, and you effectively have no idea who to call because you don't have the insurance information.

Next, just because you obtain the insurance information (either at the scene or via the police report) doesn't mean the other party actually had insurance.  According to the Insurance Research Council, about 15% of all California drivers are driving without insurance.  Truth be told, I personally believe the number is higher but that's simply based on my unscientific anecdotal experience.  In any case, don't assume the other party had insurance because there is a chance they did not.  

Why don't people have insurance?  Well, perhaps it costs too much and they've decided to forego the expense. In other words, they are taking the chance of driving without insurance.  For some people, the cost of auto insurance is simply a financial burden.  So they roll the dice and play the odds.  Also, some folks don't have insurance because they forgot to pay their premium on time.  In the meantime, they later find out their insurance policy had been canceled due to nonpayment of premium.  

Also, perhaps the driver was engaged in fraud or deception with their company.  I once had a case once where the responsible driver and his passenger decided to switch seats before the police arrived.  Apparently, he wasn't supposed to be driving and he was concerned the police would catch him in the act.  Well, since they changed seats and gave the insurance company false information, the insurance company later decided NOT to cover them for the accident since they had lied to the company about who was driving.  

In some cases, coverage may not be available if the person was engaged in a commercial activity.  For example, I had a case once where the responsible party was delivering a pizza for a local pizza restaurant.  He had the pizzeria sign on his own personal vehicle.  The insurance company decided not to cover him because he was engaged in a commercial activity (delivering pizzas), an commercial activities were prohibited by his policy.  His insurance policy only covered him for personal use of his vehicle - not commercial use.   Sometimes, insurance coverage is pulled if they find out the person driving wasn't supposed to be driving that particular car - he or she was an excluded driver on the policy.

The moral of the story is to make sure you have plenty of "uninsured motorist" coverage on your own auto policy because there is a decent chance the person who caused the accident may not have any insurance for one reason or another.  Just because you are presented with "proof of insurance" at the scene of the accident doesn't actually mean the person had insurance. It's certainly a good sign, but there's no guarantee.