I hate the term "ran it into the ground" as I find it's used too many times as a catchall. Whoever bought it might have done the best they could and never lost a single customer but had to pay off the loan on it as well as take a living from it and there just may not have been enough business to do both.

I've seen this case many times over. Someone finds a nice little mom and pop business with the owner wanting to retire. They get a loan to buy it without realizing that most small businesses only provide enough profit for the owner to make a modest living. The existing owners did okay because they had paid the business off many years before. Someone comes along, figures it's a great deal, gets the loan, only to find that there isn't enough left over after making the loan payments to live on.

I would encourage you to use any good businessplan outline and develop a businessplan. By adapting any plan outline to the drive-thru will make you more familiar with the business. If you can, try and find out the two previous owners and speak to them about why they think if failed, and then determine if you can overcome the obstacles they faced.

I got to know a guy years ago that had a Seven Eleven store. He was always complaining about how he only made a living out of it. It was a busy location but margins were lower than he thought, partly because of the franchise fees he had to pay to Southland Corp at the time. If you're not going to be part of a franchise system you'll have a certain edge on margins by being able to shop your purchasing around...this should help.
Hope this helps...