So I thread the other thread and my comment here seems to have been bang on. Larry has mentioned there that he had no shirt or helmet, and was racing to keep up with a group. What I missed was that he stopped to smoke some weed, and whilst a few people in the group got flats, most were fine and only Larry went down.
He then cycled to work the next day, got sent home and then went on a detour. So he doesn't appear to have been that injured.
After the incident, he moved a warning sign with the blessing of some road workers. So it was an active work zone with at least some signage.
So I'm not actually sure what Larry thinks he could sue for.

The whole thing also seems to have happened a month ago.

Did I miss anything?