what to do when you run out of plot points?

You can't, really, unless it's an intrinsic part of the story. If it's just travel across time and land, then put in your dots and said, "After two days in the car, both X and Y were smelly, cranky and ZZZy. Then, the dragons swooped down, and the murders began."

A car trip can be a great place to reveal characterization and do some info-dumps in the form of a conversation, but an even better way to reveal characterizations and explain things is to have your characters doing something interesting.

EDIT: in the first draft, sure, Put them in the car and be boring. You might learn something very important about them and the plot. But be aware that this is just "worksheet area" -- you will probably cut out the car scene, and just weave the important stuff in the action parts of your book.

A few years ago, I took a 30 hour train ride across China. I booked a berth in a sleeper car where I bunked with three Chinese fellows. None of them spoke so much as a word of English and I spoke not a word of Chinese. It was however a very interesting trip. I've used the experience (and others that I've accrued over the course of my life), to assist me in situations where two characters in a story that I'm working on who don't share a common language need to communicate. I've written about English encountering Algonquians in the New World, Dutch encountering Koreans in the 16th century, and French encountering Sub-Saharan Africans in the period between the World Wars. I can claim true fluency in only one language and passable proficiency in several others, but that hasn't stopped me from travelling to quite a few countries. Verbal communication isn't the only form of communication that we have as human beings. And you would be absolutely astonished how well two people who don't share a common language can communicate when the situation calls for it. While I can see that it might be a difficult scenario to script if you've never had any first-hand experience with anything like it, it's definitely not something that can't be done. As a matter of fact, it's something that happens every minute of every day, all over the world.