I have been removing Penn DOT line paint from vehicles for about 12 years.
I use lacquer thinner along with my high pressure
soap in my SS car wash bay.
I've tried most other products, but have found this to be the safest way.
The trick is to try and dissolve the line paint without hurting the cars finish.
Once all of the heavier paint is off the vehicle, you can use a clay bar.
You have to soften the paint before you use the clay bar.
The state changed their formula about 5 or 6 years ago because of voc's.
Before the change, I was able to use the car wash itself for 95% of the jobs.
Now, I have to use the thinner, the car wash, the clay bar, plus elbow grease.
Unless you know what you are doing with something like toluene, you can ruin a paint job in no time.