My teens have Life360 on their phones. We have made it a condition of us paying their phone bills, but when they're 18 they can uninstall it if they wish. DD18 is off at uni now, and chooses to keep Life 360, as she says it helps her feel safe to know that we can check where she is, or can send help directly to her in an emergency.
I would be really shocked by the speeds reported @DeadMansBones, but it's worth noting that Life360 includes any use of a mobile phone as a "risky incident", so if any time your DS (as a passenger) so much as unlocked his phone, clicked on anything etc., each would have been recorded as a "risky incident", along with things like heavy breaking, or breaking the speed limit by the driver.
I think we've been lucky so far, in that DD18 has only female friends who have passed their tests, and although she went on one 2hr journey with an 18 year old driver, it was quite sedate. We've had many conversations about the dangers of inexperienced drivers, and I always make myself available for lifts, no matter the time of day or night.
My DDs would be terrified if one of their friends drove at 100mph, so I wouldn't have to do much convincing to stop them accepting lifts going forward, but if your DS "didn't even notice", I would probably resort to showing him some news stories and stats from the last 10 years or so, showing how many teens, particularly boys, are killed on the roads by inexperienced drivers each year. I really hope he listens @DeadMansBones, you must have been terrified.