I was thinking the same thing. A front end loader would do the trick. If they get maimed in the process, BFD. Playing on the freeway, expect to get hurt.
I would think that someone’s arm immersed in concrete would suffer some serious problems. With the temperature on I-93 at about 15 degrees at that time of the morning, circulation to the limb would suffer. If the concrete was not dry by the time of ‘deployment’ then the effects would be worse because under 50 degrees the concrete won’t cure properly and would freeze...making it one very painful experience. Possibly resulting in the loss of the limb.