Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for acquiring image data, determining that the user's vehicle is traveling in a left lane of a roadway having at least two lanes for travel in a first direction, detecting that a second vehicle is traveling within a predetermined distance in front of the user's vehicle and in the left lane of the roadway, obtaining speed information of the user's vehicle and the second vehicle at a first time and at a first location, determining, based on the obtained speed information, that a speed of the second vehicle at the first time is below a defined speed limit of the roadway at the first location, and in response triggering a potential violation procedure.