I must say, I don't understand the original thought of splitting a 10' wide driveway side to side. That doesn't even make any sense to me. My driveway is 19' 6" wide and it isn't split side to side at all.

My old drive was 16' wide and was split side to side, and it was spreading apart, I think each side was allowed to lift and drop separately as the weight of vehicle traffic crossed the two pieces, and as the cement rocked against each other they pushed themselves apart. Your driveway only being one vehicle width wide, I think the problem would be compounded. Since the entire driveway isn't spreading consistently, I suspect there may be water issues under the drive at the points it is spreading more.

Unfortunately, I don't see a permanent solution, short of replacing the areas that are spreading. I wouldn't even consider that with only an inch of spread, fill the gap. Its been there 16 years and has only moved apart an inch, if it continues at that pace, in another 16 years it may be a 2" gap, but you have had things done to slow the change, it may not move any more.

Truthfully, I'm pretty impressed that a 16 year old 600' driveway isn't cracked! My 15 year old 88' driveway has a couple of very small cracks in it. Gene