While an EMERGENCY landing on a public road is not illegal,
That's what the FAA would say. Local authorities may have a different
idea. I believe it is CT that doesn't permit aircraft to land on public
property. Even in a balloon, we have to worry about tresspassing and
always get the land owner's permission ASAP. Applying the traditional
bottle of champagne minimizes gripes, also.

Once we found ourselves in a 20 kt wind, which is really moving. We
were low on fuel and had to get it down. The very experienced PIC
decided to use the drop line to catch a tree limb to stop the forward
motion so we could let it down in the only yard big enough. We had to
fight the wind and the dropline was jammed in the trees. Neighbors were
panicking and calling police and fire even though all we needed is a
little time to free the balloon. About 10' AGL the line slipped through
my hands -- no knot in the end as a line on a sailboat! So a quick rip
landing got us down. This left us dealing with the police. "Are you
guys legal? This can't be right. You must be breaking some law!" By
then the crew had taken a pix of the owner in the basket with the wine.

So it was an "Emergency" (actually several of them). The FAA would not
have complained, but the local police were all set for action.