Some Measured Distances (update)
If anybody is interested, the distance around the 7th/8th Ave subway stop on the F line is 1433 feet or 0.271401 mi. I measured it twice and got the same 1433 feet so I assume I got it correct. If you cut the corners, you can call that loop a quarter mile. It never rains or snows down there and if you ask nicely, the token clerk might hold your sweatshirt. It is not recommended that you run there during rush hour. It is not really a running place so the Prospect Park Track Club is not really encouraging anybody to run there. You might not actually be legally allowed to run down there, but it has been done. You might get some sort of ticket, so don't blame the Prospect Park Track Club if you do. So if you wanted to know how big the loop is, it's that big.
A more acceptable place to run is the amoeba-shaped running surface around the plastic grass in Columbus Park (Cadman Plaza). I measured it today at 2103 feet or 0.398295 mi. There was an inch of snow on the ground when I did this so I might be off by a foot or two. (Update, I just got word that the Parks Dept measured that loop at 2164 feet or 0.409848 miles. I guess it is shorter in the snow.)
I also measured the distance of the span of the Brooklyn Bridge. I started at the Manhattan side. There is a small patch of shrubs just before you get to Park Row. Between the shrubs and Park Row there are two plaques. I started between the plaques and ended where the pedestrian path splits to go to Cadman Plaza or towards Tillary Street. That distance is 5714 feet or 1.08219 mi. If you choose to run loops of the towers, that distance is 1630 feet or or 0.308712 miles.
I did not bring a pen so I took photographs of the wheel. As you can see it was snowing, I cannot vouch for the accuracy of this measurement. The wheel rolled over snow, salt chunks and the bridge. At best it is mostly made of bumpy wood.
Above is from Park Row to the Manhattan Tower
Above is the continuing measurement at the yellow line in the middle of the bridge
Above is the continuing measurement at the Brooklyn side of the Brooklyn tower
Above is the final measurement where path splits.