The rootball is on the right of the picture, I believe...
I'd do like others have suggested and cut off the stuff to the left of the bridge first, and let it fall down, out of the way, which will also relieve some pressure on the left side of the bridge.
Next, I'd move about 32" in from the left (I cut 16" firewood, so 32" would be two widths for me), cut down from the topside no more than 1/4 of the way through the log to avoid a pinched bar.
Finally, I'd cut up from the bottom the rest of the way, being careful and going very slow so as to be able to see how the log will start to bend down as the bottom cut starts to open. Hopefully, the log will just set down onto the bridge, and the whole thing with rootball won't come sliding down the hill at you. It probably won't, but hey, pretty much everything unexpected can happen. Caution is your best friend.
Then repeat again until you have cleared the left side of the bridge.