Let's make it clear that as much as we bash McDonald's, we will praise them when they do well.
According to the CSPI, despite the fact that New York City banned trans fats, you are still getting some in your French fries. But in the CSPI test where it had independent laboratory analyze the samples, McDonald's did significantly better.
Burger King scored 3.3 grams of trans fat and Wendy's had 3.7 grams of trans fat, while McDonald's had 0.2 grams of trans fat. (Wendy's did have a significantly larger amount of fries.)
You are asking: "Gee, they banned trans fat. Why is it still there?" The likely answer is that partially hydrogenated oils are being used in the par-fry process, where French fries are pre-fried before they are shipped to the restaurants.
While technically fulfilling the law, Burger King and Wendy's are certainly violating the spirit of the law. And consumers are getting misled.
Kudos to McDonald's for doing it right in NYC. Now, do it everywhere else and we'll truly be happier.