Seemingly plagued by bad luck (or at least homicidal automobiles), Lumpy is run over by the Chosen One when they arrive at Broken Hills in the Highwayman. This isn't the first time Lumpy has been in an accident involving automotives either - before the Great War, he claims that he personally caused a Nuka-Cola truck to crash, sending bottle caps everywhere...
He then leaves the town indefinitely, no matter if the Chosen One chooses to help him from under the car or not (where he will be gone after a zone change).
If it is your first time visiting Broken Hills in the Highwayman, you will unavoidably end up hitting Lumpy with the car, and he will be lodged beneath it. You end up seeing him under the grill of the car after you park. You can then talk to him while he is beneath the car and choose whether to help him, or not.
The Line "I'm coming to meet you Elizabeth!" maybe a reference to Sanford and Son where phrases such as "I'm coming Elizabeth!" and "You hear that, Elizabeth? I'm coming to join ya, honey!" were said when he fakes a heart attack.