-->
This particular interpretation of the phrase taqta'un as-sabil is advanced by Baghawi and (on the authority of Al-Hassan) by Zamakhshari; Razi adopts it exclusively and without reservation.
They infested highways and committed their horrible crimes not only secretly, but openly and publicly, even in their assemblies. Some Commentators understand "cutting off the highway" to refer to highway robberies: this is possible, and it is also possible that the crimes in their assemblies may have been injustice, rowdiness, etc. But the context seems to refer to their own special horrible crime, and the point here seems to be that they were not ashamed of it and that they practiced it publicly. Degradation could go no further.
This is another instance of their effrontery, in addition to that mentioned in vii. 82: the two supplement each other. Here the point emphasised is that they did not believe in Allah or His Punishment, and dared Allah's Prophet Lot to bring about the Punishment if he could. And it did come and destroy them.