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 Massachusetts, laws governing unsafe lane changes are outlined in the Massachusetts General Laws, specifically in Chapter 89, Section 4A. This statute requires drivers to use turn signals when changing lanes and mandates that lane changes must be made safely. A driver must remain within a single lane until it is safe to move into another lane, and they must not cross multiple lanes of traffic at once. Failure to adhere to these rules can result in a traffic citation, which typically includes a fine and may also result in demerit points being added to the driver's record. The amount of the fine and the number of points can vary. Law enforcement officers have discretion in issuing citations, and prosecutors have discretion in pursuing charges. If a case goes to court, it is up to the judge or jury to determine if the prosecution has met its burden of proof to convict the driver of a criminal offense or find them responsible for a civil infraction.