Used to describe someone who is barely hanging on with little left in their personal gas tank. Their slightest bit of hope, oftentimes irrational, is the only thing still driving them. All the person needs to do is stop and fill up their tank but they keep pushing it through the next exit and the next exit until they eventually run out of gas on the desolate highway.
Person A : "Todd hasn't made a sale in 2 years and he works on a commission only basis. He thinks his next deal is close though and will be a huge payday."
Person B: "Yeah, he's running on hope fumes."