As a solo roadtripper, I would not want to have a stranger in my vehicle...... ever. I like the (selfish) luxury of being able to stop, turn, spend time or just continue without having to consider the needs/wishes of another.
However, solo does not mean always being alone. It affords a great opportunity to interact with fellow travellers and the locals wherever one is. Sometimes asking a question could get one in a conversation with a total stranger - even if one already knew the answer to the question.
When having a break, don't always sit down at an empty table... ask another lone guest if you may share their table. This is getting harder and harder to do, as folks are generally engrossed in their electronics, and may not even notice others around them.
Showing an interest in something unique about the travelling party parked next to you, even at a rest area, can be a great way to meet people. Only a week ago I was at a truck stop and parked near another vehicle identical to mine (a year older). Got to chat with the owner who came from Tennessee and spoke with a broad Scottish accent.
We shared improvement plans to our vehicles and inspected what had already been done. Before departing, here were two strangers who 60 minutes earlier had not met, saying goodbye with a big hug in the middle of the parking lot.... in the rain. Of course we exchanged contact details. Who knows, we may meet again... one day.
Keep a daily journal.... you'll be surprised how many people you meet, how many
places of interest you visit. But you will forget if you do not write it down.
Lifey