A traffic accident was an incident involving vehicles and their occupants in which the vehicle in question malfunctioned or crashed.
Some accidents resulted in death. In 1930, Edith Keeler died in a traffic accident after she crossed the street to find out why James T. Kirk had left her abruptly. Her death in this manner was detailed in her obituary, one of her two possible futures (the other being her rise in influence after being saved from that same accident by Leonard McCoy following his cordrazine-induced trip through the Guardian of Forever). Despite his love for Keeler, Kirk kept McCoy from saving her, thus ensuring that the timeline would not be damaged. (TOS: "The City on the Edge of Forever")
In 1968, Agent 201 and Agent 347 were killed in an automobile accident on Highway 949, ten miles north of McKinley Rocket Base, necessitating Gary Seven's takeover of their assigned mission. Upon hearing of it from the Beta 5 computer, he found it incomprehensible that such a "useless" event would eliminate them and asked for verification, which he received. (TOS: "Assignment: Earth")
In 2000, Shannon O'Donnell rear-ended another car after asking a passerby for directions to the Millennium Gate. When the driver asked for her insurance information, she said it had run out, nor could she pay for the damages in cash. After the driver left, O'Donnell found that her car wouldn't start. She sought refuge at Alexandria Books while waiting for the tow truck. (VOY: "11:59")
In 2376, while playing the Fair Haven holoprogram, Tom Paris crashed his horseless carriage and lost a wheel. He attributed it to his having "zigged when I should have zagged." Later, when Harry Kim brought up Paris' "little traffic accident", Paris attributed it to a clutch malfunction. (VOY: "Spirit Folk")