There are lots of legal differences - I'm not sure what you mean.
You can't sue the council if you trip over a raised flagstone and hurt yourself;
The council can't make parking orders and the parking wardens have no authority;
The council won't maintain it;
Nobody except the owners have the right to use it or park on it.
A highway is a public right of way. Either by carriage, horse or foot, depending on the category.
Without intending to get picky with Ethel's good answer, a small number of private roads are maintained by the council under an agreement with the landowner. And other landowners (other than the landowner whose land the private road is on) may have acquired a legal right of way over it.
Thanks for the replies
I live on a private unadopted road and wanted to put up
no entry signs with the permission of all residents
the highways told me that I couldn't but I have been told by Highways on E.mail that a Private rd "residents only" sign is acceptable
I dont understand the difference
Dave
I suspect it is because a 'No Entry' sign is a highways sign and has a legal standing. That much said, there are many privately owned sites - MOD for example that use highways signs to direct traffic around them willy-nilly. But they are probably regarded as a special case.