A siren goes off behind you. That light was yellow, you are certain. The officer who comes to the window disagrees. She takes your license and registration, goes back to the squad car for an excruciating ten minutes, and returns with a citation.
Getting a ticket is an imposition and an expensive lesson, especially if an insurance rate hike is included. But it's also often a criminal infraction, a category that covers a rather large amount of misconduct.
Whether an offense is an infraction or misdemeanor is a matter of degree. Criminal infractions are the least serious class of crimes, and they fall below misdemeanors, which are less serious than felonies.
Infractions include things like moving violations and other low-level misconduct. Other names for infractions include petty offenses, violations, and (not to confuse things) petty misdemeanors. In general, the penalty for a criminal infraction is limited to a fine and doesn't lead to jail time.
The most common type of infraction is a traffic violation, such as speeding, running a red light, and failing to signal a turn. (More serious vehicular offenses, like driving under the influence or a hit-and-run, are considered crimes and carry the potential for time behind bars if convicted.) In addition to driving infractions, jaywalking, loitering and, in some jurisdictions, possession of small amounts of marijuana (in states where it's illegal) are other examples of criminal infractions.
Although a stop for an infraction isn't as serious as a criminal arrest, it could give the police an opportunity to escalate the stop into an arrest or search, which could lead to more serious charges.
In general, a police officer can't conduct a search based simply on the stop itself. But if the officer sees, smells, or otherwise observes something during the stop that gives them reasonable suspicion of criminal activity, the officer can search. For example, if during a stop officers notice drugs on the console, they can probably search the car for additional drugs.
A few states allow police officers to arrest individuals stopped for criminal infractions. Upon arrest, an officer can conduct a brief frisk (or pat-down) if they reasonably suspect the person might be carrying a weapon. But an arrest usually doesn't give officers the right to search the car unless they have reason to believe the vehicle contains weapons, evidence, or contraband. One exception is that officers can search areas in the car within the arrested person's reach.
If an officer notices evidence of a crime during a stop for an infraction, the person stopped can be charged with that crime in addition to the infraction. For example, when an officer stops a driver for running a red light and then smells alcohol on the person's breath, the officer can probably arrest the person for driving under the influence (though the mere odor of alcohol isn't likely enough for a conviction).
Also, officers almost always run a license check when they stop someone for an infraction. For most people charged with driving with a suspended or revoked license, the crime is discovered when they're stopped for an infraction. Outstanding arrest warrants are often discovered during traffic stops, too.
Criminal infractions typically carry a fine but no jail time. A conviction for certain kinds of criminal infractions can be expensive, both in the amount of the fine (and surcharges) imposed and in the effect the conviction may have on insurance rates. Courts will sometimes allow those convicted of criminal infractions to attend traffic school or other programs, which might reduce the financial impact of the conviction.
Ignoring an infraction can lead to an increase in the fine amount and, in some instances, to an elevation of the charge to a misdemeanor, which carries potential jail time. In some states, an infraction can be charged as a misdemeanor if the person has been convicted of multiple infractions within a certain amount of time.
Often, you can just pay the fine for a criminal infraction, and it'll all be over. Paying the fine is an admission of guilt, and will likely increase your insurance rate. If you want to fight the ticket or citation, you'll need to go to court.
Because there is no risk of incarceration, some courts treat infractions like civil actions and even hear them in civil courts. As a result, the prosecution's burden of proof might be lower than it is in a criminal trial. It also means you might not have a right to a court-appointed attorney, though you can hire a private attorney to represent you.
Sometimes it's possible to respond to a criminal infraction by paying it or by going to court without hiring an attorney. But if you have multiple tickets or believe the stop wasn't justified, consider consulting with a lawyer. And if you've been charged with a misdemeanor or felony arising out of what began as an infraction, you should talk to an experienced criminal defense attorney as soon as possible.