“I live in Maine and have house with a deeded right of way through someone’s property to get to my house. My deeded right of way is stated as 50 ft. My driveway is very narrow, only about 8 ft. wide. Could I tar the rest of the 50 ft. if I want? What are my rights?”
It depends first on exactly what is stated in the deed that created the right-of-way. Does it specify what kind of driveway you were granted? Does it state who is responsible for maintenance costs?
If there’s no clear guidance in the creating document, then your next place to look is your local laws and court decisions. You will need to consult with a local attorney to review these and see if they have any guidance on the matter.
As a practical matter, however, you probably don’t want to get into a lawsuit with your neighbor over this issue. I would suggest starting by talking with your neighbor about what you want to do and exactly where within the easement you would put the extra pavement. Very few people need a 50-foot-wide driveway, though as you say 8 feet is a bit narrow. This gives you a lot of room for negotiation.
You should not, however, do any construction outside of the area of the deeded easement without having a written agreement (or another easement), since that could lead to trouble in the future, especially when your properties are owned by different people who weren’t around when you had this discussion.