A written warning for a driving violation is a way for the officer to remind you of your violation without issuing a formal citation. Unlike a citation, it does not appear on your official driving record. For this reason, you don't have to worry about how long a written warning stays on your license.
The Point System
Each state has its own rules of the road, and the number of points assessed for a particular violation may vary state to state. However, the vast majority of states use a point system to keep track of the number and severity of offenses committed by a driver. Each type of violation – whether it's speeding, running a stop sign or something else – is assigned a set number of points. Usually the more serious the violation, the more points the violation carries.
Points and License Suspension
Accumulate enough points on your license in a specified length of time and your license may be suspended. When you are issued a citation for a driving violation, and that citation becomes a final conviction of the violation, the points carried by that violation attach to your license. If you fight the citation in court, you may be able to convince the court to withhold the points from your license even if you don't beat the citation. A written warning is not a citation. It does not attach to your license.
States Without Points Systems
Nine states don't use the point system, but violations for which you are issued a citation still attach to your driving record. These states use your driving record, rather than the tally of points on your license, to decide if your behavior as a driver warrants further disciplinary action.
Points and Insurance Rate
The more points you have on your license, the greater risk insurance companies consider you to be. Having points on your license means you committed a violation. Insurance companies typically take that to mean you're likely to commit more violations in the future, perhaps ultimately requiring the company to pay a claim against your policy. This is why your auto insurance rates are likely to increase once points attach to your license. The more points you have, the more likely you are to cost the insurance company money in the form of a claim. However, because written warnings do not carry points and are not reflected on your driving record, they are not reported to your insurance company. Thus, there is no opportunity for a written warning to cause an increase in your insurance rates.