DOT in NC plants this along many highways, and I have seen it in neighboring states, too. Then they have to request funds to cut it back or poison it. Makes no sense.

I would create, if practical, a barrier where you mow the plants between the crown vetch and your property. Mowing short will slow the spread of crown vetch, and you can visit several times a summer and spray any plants in the barrier zone with Roundup to kill them. This is a pain, but better than Crown vetch all over your property.

NC we have it planted along our highways too and its gotten out of control.Its even on backroads.
Lady, I would do that but its all woods, no grass along the dirt road. Its growing in with the weeds.