§ 1128(s) of the NYS VTL sets forth that a vehicle shall not be moved from a lane until the driver has ascertained that the movement can be made with safety.
Unlike the more “measurable” offenses (for ex color of a light or speed), what constitutes an “unsafe” lane change is a bit of a judgment call by the issuing police officer. There is no exact definition of what constitutes a “safe” vs an “unsafe” movement on a roadway.
In order to establish such a charge, an issuing officer must be able to offer some testimony regarding both speed traveled by the vehicle(s) in question and distance between the vehicles in question. Exiting your lane to enter an adjacent lane five feet in front of another vehicle may be perfectly safe in slow moving traffic but extremely dangerous at ordinary highway speeds.
The speed element of this violation can often be used to assist the defense, especially when the officer isn’t trained to visually estimate speed and/or isn’t trained to use or didn’t have at the time of the incident the proper equipment to measure speed.
It is not unusual to see an unsafe lane change ticket issued as a “companion” ticket to other charges such as speeding or failing to signal.
A conviction for unsafe lane change carries three (3) points in NYS.