All states have laws that prohibit drivers from making unsafe lane changes. State laws generally require a driver on a road with marked lanes to operate the vehicle within a single lane and to move to another lane only at a time and in a manner that is safe.

This means a driver may not cross more than one lane of traffic at a time, must allow a safe distance between the driver’s vehicle and other vehicles, and must signal the lane change with a blinker, as required by law. The failure to do so may result in a ticket or citation for an unsafe lane change.

The penalty for making an unsafe lane change usually includes a fine and demerit points on your driver’s license or record.

As with many traffic violations, the officer issuing the citation and the prosecutor have significant discretion in determining whether there was a violation of a traffic law and whether the violation constitutes a certain offense, as defined by the state legislature in the traffic code or in a municipal ordinance.

This discretion to issue a ticket or citation and prosecute the charge against the driver is balanced by the discretion of the jury or judge in determining whether the prosecution met its burden of proof sufficient to convict the driver (for a criminal offense) or find the driver responsible (for a civil infraction, violation, or offense).

In Missouri, drivers are required to adhere to laws that mandate safe lane changes. According to Missouri state statutes, a driver must remain within a single lane and only change lanes when it can be done safely. This includes not crossing multiple lanes of traffic at once, maintaining a safe distance from other vehicles, and using turn signals to indicate the lane change. Failure to comply with these rules can result in a citation for an unsafe lane change, which typically carries a fine and may add demerit points to the driver's record. Law enforcement officers have the discretion to issue citations, and prosecutors decide whether to pursue charges. However, a judge or jury ultimately determines the outcome of the case, deciding if the prosecution has proven the driver's violation of the law beyond a reasonable doubt in criminal cases, or by a preponderance of the evidence in civil infractions.