Hi,
I have recently found this quirk, either is a bug or the highway documentation needs to be updated, how to remove pavement from highway without destroying it:
1. The pavement has to be laid on a very thin dirt layer.
2. After a dig actions to remove all dirt, the border has to be not flat, so you can level.
3. Level, the pavement will be destroyed and the rock layer exposed. If you try to dig all around of tile you wiill get a standard "You can't dig in solid rock" error.
4. After dropping a dirt you will get dirt.
Highway seems to be functional after this operation, so I left it for you to investigate, it is West of Elysium Bay on Independence, nest to Karkinos deed.
Screenshots: