If you drive from  er I remember being stopped by one of those men in the dark glasses erm  if you drive from Maine  into New Hampshire  the speed limit in Maine is sixty five and the speed limit in New Hampshire is fifty five  and you just cross a si er y there's a signpost which says welcome to Maine or New Hampshire, whichever way you're going, and the second you cross that line, theoretically, you have adjust to the different speed limit.