Most people go their entire lives without hearing about an SR22 insurance policy. This is a very good thing. You do not want to know about this until you have to, and if you are ordered to get such a policy, it is probably because you fall under one of the following reasons for requiring it.
You Were Convicted of a DUI
It does not matter if the DUI ticket and conviction was for alcohol or for drugs. It does not even matter if it was prescription drugs and you have a note from your doctor. If you were convicted of a DUI, a judge can order that you get SR22 insurance, or lose your license for the period of time he/she has stated. Since most people cannot go without their license, they will go get the SR22 insurance policy.
You Had Your License Suspended Because of Too Many Accidents
Car accidents, regardless of type, result in demerit points off your license. For most states, that is somewhere between twelve and twenty demerit points. If you lose all the points on your license, your license is suspended. You cannot drive. If you drive with a suspended license and you are caught, your license is revoked. Then you will definitely be required to get SR22. All accidents resulting in demerits, suspension of license, and revocation may result in a judge ordering you to get SR22. These policies are not cheap, either, and the cost is painful enough for you to remind yourself to be much more careful while driving.
You Caused a Car Accident That Resulted in a Death
If you cause a car accident that results in death, be grateful that the judge only orders you to get the SR22 policy. Usually, it means loss of license, jail or prison, house arrest, and/or the requirement of SR22 once the rest of your sentence is carried out. A completely accidental death that had nothing to do with a DUI and was just a freak occurrence is where this "lighter" sentence might result. Vehicular manslaughter, or intentional murder by car, is a different story.
You may find that you are not allowed to drive for years after you complete your jail sentence, and even then you might still be required to get the SR22 before your license is returned to you. As you can see, none of these scenarios are typical of most drivers, which is why you only hear about SR22 when you absolutely need it and are told by the judge that you have to have it.