The option to track trips and mileage per vehicle is unavailable in meantime. I'll send this feedback to our engineers to have a report that we can run to keep track our personal and business trip for each vehicle used. We can check out our QuickBooks Blog to get check on what's new with QuickBooks.
For now, we can open each added trip and manually take note of the information including the vehicle. I'm also adding these articles for more information about mileage tracking: