A man believed to be brandishing a weapon tried to get into a lone woman driver’s car late at night.
But before the man could force his way into the vehicle the motorist managed to drive off.
The frightening incident happened between Gallows Hill and Upper Highway in Abbots Langley just before 11.30pm on Tuesday.
A spokesman for Herts Police said: “It looks like she did the right thing - driving off and reporting it to police.”
The man is described as white, around 5ft 10in, aged in his late 30s with short dark hair. His description has been circulated to police officers in the area.
Anyone with information can contact police on the non-emergency number 101.