Thank you! :-)
This was a jam-game (done in 2 days), so it lacks a lot of features: rotate the opposite way, roads that 'snap'/look nice, lose-condition check(s), and, yes, the highlighting. (Also smaller maps, hi-score table, save feature, undo, ...)
I'm not really working on it at the moment, though. Sorry :-( If I ever decide to upgrade/sequel one of my games however, it'll be either this one or Arcade Overflow, so who knows.
P.S. On the off-chance you (or anyone else for that matter) knows C++: The source-code (which is a terrible mess) is available, so it might be possible to hack it yourself.