The incident happened in the area of Stankards Road, Uphall, at the junction with Maclardy Court between 12pm - 12.30pm on Tuesday 23 February.
The male suspect was in the passenger seat of the car and assaulted the female driver.
It’s possible that two passers-by may have witnessed the incident, which occurred in a red Ford Ka with black racing stripes around the middle of the vehicle.
The first witness is described as a white woman, in her 50s, around 5ft 7in tall with a medium build and blonde/greyish shoulder length hair.
The second witness is described as a white boy, around 15 to 16-years-old, 5ft 7in tall, skinny build with short dark brown hair.
He was walking a small white dog.
Detective Constable Allan Herbert, of Livingston Police Station, said: “We’re appealing for anyone who witnessed this incident to come forward, particularly the two witnesses mentioned above.
“The red Ford Ka with black racing stripes is very distinctive, and it’s possible they may have heard a woman screaming from within the car.”
Those with any information can contact Police Scotland on 101 or alternatively the charity Crimestoppers anonymously on 0800 555 111.