Good question. It cannot be very large as it wouldn't fit otherwise. Which OS do you use? Is it Kirigami version?

I am running PostmarketOS on PinePhone.

PostmarketOS being derivative of Alpine Linux, the PureMaps package I run was installed from Alpine package repository

Does it clarify?

It should be the same font as is used on the phone by default. Try to increase that in the system and it will increase accordingly.

I guess there would be a limited number of people willing to change their system font to large before each drive and then change it back to normal afterwards? Any chance of this becoming a preference setting within the application?

In principle, it can become preference. Similar to what we have already in terms of map font sizes that depend on the mode as well (map viewing, navigation by car, ...). Just it needs an idea how to integrate it well and making it. Not sure when I can look into it.

I also support this request. I took my phone for a spin today and I could hardly see the ETA due to the tiny font.

Right now I am busy with other projects, but will find the time to review submitted code changes if they land to support such feature.