A couple of plants at the roadside:
Garlic Mustard (4 white petals) – considered very invasive in New England. Lots of tenacious runner/rhizome roots, tough to eradicate.
Poison Ivy (three early shiny leaflets and eventually thick, climbing vines on trees)
Western Poison Oak is another species in the same genus.
Some people call Poison Ivy, Poison Oak though they are generally referring to poison ivy.